devel/geany-plugin-git-changebar: Fix build with libgit2 1.5.0

Import patches from upstream master branch to fix build with recently
committed libgit2 1.5.0.

Reported by: fallout
Obtained from: https://github.com/geany/geany-plugins/commit/668f5d07eef16e227402eab09141c738b315d94b

		https://github.com/geany/geany-plugins/commit/5d9f1bc6d010e6b4c6a21af8a39b90922f89a82c