Reduce JGit memory use

[jimbethancourt]

trafficstars

The memory needed by JGit may be able to be reduced by discarding the body of the commit.

RevWalk walk = new RevWalk(repository);
walk.setRetainBody(false);

See https://wiki.eclipse.org/JGit/User_Guide#Reducing_memory_usage_with_RevWalk

[patomos]

I can also work on this issue

cc: @jimbethancourt