This JGit version brings significant performance improvement in the case when
Gerrit loads all external-ids from NoteDb. This happens whenever the
external_ids_map cache gets invalidated or expires.
With NoteDb containing about 70K external-ids we measured the following
times for loading all external-ids:
* Using JGit without [1]: 10 seconds
* Using JGit with [1]: 2 seconds
[1] https://git.eclipse.org/r/150254
Change-Id: I70c7f0d207ab9baa283fdda8432a2fc5e633553a
49dcef02c2