Add the "jgit diff" command This commit contains fixes provided by Christian Halstrick. Bug: 291083 Eclipse-CQ: 3559 Change-Id: If8d187e70a51f31040f99098489e513791dc6415 Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>