Start the merging-rebase to v2.10.0-rc2

Let's prepare already a little earlier for the upcoming release (which
is due September 2, 2016, according to https://tinyurl.com/gitCal).

In particular, the now-obsolete cat-file-smudge branch was ripped out,
leaving only the cat-file-filters branch in (which should become part of
upstream Git in one way or another).

Also, we lose the duplicated common-main patches that were still in Git
for Windows' fork.

The two biggest changes, though, are that the git-wrapper was moved out
of Git for Windows' git.git fork (and into the MINGW-packages
repository), and the rebase--helper patches that are still under review
on the Git mailing list will most likely be integrated so that Windows
users can benefit from the noticeable speedup (5x in this developer's
measurements).

This commit starts the rebase of db1c6ea to 32ce570

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho