Prevent git from using pager if content less than one screen

http://stackoverflow.com/questions/2183900/how-do-i-prevent-git-diff-from-using-a-pager

Passing the -F option to less causes it to quit if the content is less than one
screen, however after doing so the screen is reset and you end up not seeing
the content, the -X option does away with that behaviour. So, I use the
following to enable conditional paging based on the amount of content:

    git config --global core.pager less -F -X

Signed-off-by: Kare Nuorteva <kare.nuorteva@me.com>