* tests/symlinks: Add more path traversal test cases.

* src/safe.c (struct symlink): A symlink to resolve.
(push_symlink, pop_symlink): New functions.
(read_symlink): Create a new symlink stack entry.
(traverse_next): Follow ".." components within the working directory. When
hitting symlinks, "follow" them by reading and returning them.
(traverse_another_path): Recursively traverse symlinks.

When a file has already been renamed, make sure it is not renamed back to its
old name.  Reported by Guido Draheim.
* src/patch.c (main): Make sure we never rename a file back to its previous
name. Report when a file was renamed already.
* tests/copy-rename: Add "already renamed" test cases.

* src/safe.c: Include util.h for say(). Define EFTYPE if it isn't defined
already.
(traverse_another_path): When openat fails, also check for EMLINK, EFTYPE, and
ENOTDIR. Change the error message to "file ... is not a directory" and only
skip the rest of the patch instead of aborting.
* tests/symlinks: Update.

Reported and fixed (mostly) by Christian Weisgerber <naddy@mips.inka.de>:
* tests/deep-directories: Avoid the bash >& redirection operator.
* tests/no-mode-change-git-diff: Instead of "stat -c", use "ls -l  sed".
* tests/read-only-files: A redirection failure for a special built-in causes
some shells (FreeBSD sh, OpenBSD sh (pdksh), some bash --posix) to exit, and
the colon command is a special built-in. Perform the redirection in a subshell.

* tests/symlinks: Check the result of treating a symlink as a file with
--follow-symlinks.

Diffs can be indented by a variable number of spaces, tabs, or X characters.
Make sure that intuit_diff_type() only accepts context diffs where the first
and second line are indented identically, or else another_hunk() will fail.
* src/pch.c (intuit_diff_type): Remember the indentation of the last line. Only
recognize context diff hunks with the same amount of indentation on the first
and second line.
* tests/garbage: New test case.
* tests/Makefile.am (TESTS): Add test case.

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>

Since the code is identical when just checking if a utility is present on
the system or not, we can factorize it.

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>

* tests/symlinks: Add a test case where the patch file itself is in a path that
follows a symbolic link; we want to continue allowing that.