My motivation at the moment is that I'm trying to share a
git checkout between multiple VMs using VirtualBox's Shared
Folders feature. git in the guest VM isn't able to see the
executable bits from the host due to the VirtualBox/SMB/CIFS
layer. Instead, it thinks text files are non-executable,
unless they have a shebang line. That's a sensible way to
set the flags anyway, so set them like that.
With this commit, there's still one file that isn't handled:
src/shared/GetCommitHash.cmd. It's still marked executable,
but it lacks a shebang line, so the guest thinks it's
non-executable. I'm not sure it should be changed.
