Synced with Transifex

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Prepared release and bumped version numbers to 1.8.8.0

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Updated libgit2

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Build libgit2 with GIT_THREADS defined

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