Clean up some sorting function stuff including fixing qsort_r
on MinGW, common function pointer type for comparison, and basic
insertion sort implementation (which we, regrettably, fall back
on for MinGW).

git__bsearch and git__tsort did not pass a payload through to the
comparison function.  This makes it impossible to implement sorted
lists where the sort order depends on external data (e.g. building
a secondary sort order for the entries in a tree).  This commit
adds git__bsearch_r and git__tsort_r versions that pass a third
parameter to the cmp function of a user payload.

This fixes all the warnings on win64 except those in deps, which
come from the regex code.

Signed-off-by: schu <schu-github@schulog.org>

Ensure that all memory related functions (malloc, calloc, strdup, free,
etc) are using their respective `git__` wrappers.

There were quite a few places were spaces were being used instead of
tabs. Try to catch them all. This should hopefully not break anything.
Except for `git blame`. Oh well.

1. The license header is technically not valid if it doesn't have a
copyright signature.

2. The COPYING file has been updated with the different licenses used in
the project.

3. The full GPLv2 header in each file annoys me.

Signed-off-by: schu <schu-github@schulog.org>