git-wrapper: avoid fork bombs
git-wrapper: avoid fork bombs

There has been a report that `bin/git.exe` spawns itself over and over
again. This is clearly a bug, and to avoid it from making a user's
machine sluggish, let's error out early in that case.

Signed-off-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>

git-for-windows/MINGW-packages,git-for-windows/MINGW-packages,dscho/MINGW-packages,dscho/MINGW-packages,dscho/MINGW-packages,dscho/MINGW-packages,git-for-windows/MINGW-packages,dscho/MINGW-packages