Update libgit2

(fixes issue #2216)

Signed-off-by: Sven Strickroth <email@cs-ware.de>
TortoiseGitMerge: Use the screen chars of the current view for the scrollbar page value, not the
min screen chars of all views

Based on TorotiseSVN revision 25566

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>