Start the merging-rebase to junio/maint

The changes in upstream/maint are actually not really that crucial for Git
for Windows, but we can use it as an excuse to fix the branch thicket: the
`visual-studio` branch clearly wants to be based on the
`jeffhostetler/vs2015` branch, as the latter contains important compile
fixes for Visual C, required to build inside Visual Studio.

While at it, we also move the Vagrant patches farther to the end, as they
are unlikely to be accepted upstream, so we'll try only after getting the
MSVC/VS patches in.

Also, let's reorder a couple other patches into more logical places.

This commit starts the rebase of 4638a92 to a274e0a

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

Author: dscho