Jenkins uses two plugins to implement git support.
The git-client-plugin provides low level implementation details and delivers its functionality with either command line git or JGit (a pure java implementation of a useful subset of command line git). The current version of the git-client-plugin is 1.19.6 as of 16 May 2016.
The git-plugin provides higher level implementation like optional merging, changing the base against which differences are computed, optionally ignoring commits, and more. The current version of the git-plugin is 2.4.4 as of 16 May 2016.
Please use the mailing list for support questions, rather than posting questions to closed bug reports. There are far fewer people who read closed bug reports than read the mailing list.