Add a INSTALL_SYMLINKS option which if enabled, changes the default
hardlink installation method to one where the relevant binaries in
libexec/git-core are symlinked back to ../../bin, instead of being
hardlinked.

This new option also overrides the behavior of the existing
NO_*_HARDLINKS variables which in some cases would produce symlinks
within to libexec/, e.g. "git-add" symlinked to "git" which would be
copy of the "git" found in bin/, now "git-add" in libexec/ is always
going to be symlinked to the "git" found in the bin/ directory.

This option is being added because:

 1) I think it makes what we're doing a lot more obvious. E.g. I'd
    never noticed that the libexec binaries were really just hardlinks
    since e.g. ls(1) won't show that in any obvious way. You need to
    start stat(1)-ing things and look at the inodes to see what's
    going on.

 2) Some tools have very crappy support for hardlinks, e.g. the Git
    shipped with GitLab is much bigger than it should be because
    they're using a chef module that doesn't know about hardlinks, see
    https://github.com/chef/omnibus/issues/827

    I've also ran into other related issues that I think are explained
    by this, e.g. compiling git with debugging and rpm refusing to
    install a ~200MB git package with 2GB left on the FS, I think that
    was because it doesn't consider hardlinks, just the sum of the
    byte size of everything in the package.

As for the implementation, the "../../bin" noted above will vary given
some given some values of "../.." and "bin" depending on the depth of
the gitexecdir relative to the destdir, and the "bindir" target,
e.g. setting "bindir=/tmp/git/binaries gitexecdir=foo/bar/baz" will do
the right thing and produce this result:

    $ file /tmp/git/foo/bar/baz/git-add
    /tmp/git/foo/bar/baz/git-add: symbolic link to ../../../binaries/git

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

This variable will be e.g. "libexec/git-core" if
gitexecdir=/tmp/git/libexec/git-core is given. It'll be used by a
subsequent change.

This is stolen from the yet-to-be integrated (needs resubmission)
"Makefile: add Perl runtime prefix support" patch on the mailing
list. See
<20180108030239.92036-3-dnj@google.com> (https://public-inbox.org/git/20180108030239.92036-3-dnj@google.com/).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Change the bindir_relative variable to work like the other *_relative
variables, which are computed as a function of the absolute
path. Before this change, supplying e.g. bindir=/tmp/git/binaries to
the Makefile would yield a bindir_relative of just "bin", as opposed
to "binaries".

This logic was originally added back in 026fa0d5ad ("Move computation
of absolute paths from Makefile to runtime (in preparation for
RUNTIME_PREFIX)", 2009-01-18), then later in 971f85388f ("Makefile:
make mandir, htmldir and infodir absolute", 2013-02-24) when
more *_relative variables were added those new variables didn't have
this bug, but bindir_relative was never fixed.

There is a small change in behavior here, which is that setting
bindir_relative as an argument to the Makefile won't work anymore, I
think that's fine, since this was always intended as an internal
variable (e.g. INSTALL documents bindir=*, not bindir_relative=*).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Teach parse-options API an option to help the completion script,
and make use of the mechanism in command line completion.

* nd/parseopt-completion: (45 commits)
  completion: more subcommands in _git_notes()
  completion: complete --{reuse,reedit}-message= for all notes subcmds
  completion: simplify _git_notes
  completion: don't set PARSE_OPT_NOCOMPLETE on --rerere-autoupdate
  completion: use __gitcomp_builtin in _git_worktree
  completion: use __gitcomp_builtin in _git_tag
  completion: use __gitcomp_builtin in _git_status
  completion: use __gitcomp_builtin in _git_show_branch
  completion: use __gitcomp_builtin in _git_rm
  completion: use __gitcomp_builtin in _git_revert
  completion: use __gitcomp_builtin in _git_reset
  completion: use __gitcomp_builtin in _git_replace
  remote: force completing --mirror= instead of --mirror
  completion: use __gitcomp_builtin in _git_remote
  completion: use __gitcomp_builtin in _git_push
  completion: use __gitcomp_builtin in _git_pull
  completion: use __gitcomp_builtin in _git_notes
  completion: use __gitcomp_builtin in _git_name_rev
  completion: use __gitcomp_builtin in _git_mv
  completion: use __gitcomp_builtin in _git_merge_base
  ...

Code doc update.

* nd/object-allocation-comments:
  object.h: realign object flag allocation comment
  object.h: update flag allocation comment

A doc update.

* jk/smart-http-protocol-doc-fix:
  smart-http: document flush after "# service" line

The "interactive.diffFilter" used by "git add -i" must retain
one-to-one correspondence between its input and output, but it was
not enforced and caused end-user confusion.  We now at least make
sure the filtered result has the same number of lines as its input
to detect a broken filter.

* jk/add-i-diff-filter:
  add--interactive: detect bogus diffFilter output
  t3701: add a test for interactive.diffFilter

"git worktree" learned move and remove subcommands.

* nd/worktree-move:
  t2028: fix minor error and issues in newly-added "worktree move" tests
  worktree remove: allow it when $GIT_WORK_TREE is already gone
  worktree remove: new command
  worktree move: refuse to move worktrees with submodules
  worktree move: accept destination as directory
  worktree move: new command
  worktree.c: add update_worktree_location()
  worktree.c: add validate_worktree()

"git add -p" has been lazy in coalescing split patches before
passing the result to underlying "git apply", leading to corner
case bugs; the logic to prepare the patch to be applied after hunk
selections has been tightened.

* pw/add-p-recount:
  add -p: don't rely on apply's '--recount' option
  add -p: fix counting when splitting and coalescing
  add -p: calculate offset delta for edited patches
  add -p: adjust offsets of subsequent hunks when one is skipped
  t3701: add failing test for pathological context lines
  t3701: don't hard code sha1 hash values
  t3701: use test_write_lines and write_script
  t3701: indent here documents
  add -i: add function to format hunk header

A sample auto-gc hook (in contrib/) to skip auto-gc while on
battery has been updated to almost always allow running auto-gc
unless on_ac_power command is absolutely sure that we are on
battery power (earlier, it skipped unless the command is sure that
we are on ac power).

* ab/pre-auto-gc-battery:
  hooks/pre-auto-gc-battery: allow gc to run on non-laptops