Define FileHeader.PatchType to report the style of patch used
Patches in a Git world come in at least three flavors:
* Traditional unified patch
* Binary patch with no data ("Binary files a/a and b/a differ")
* Git binary patch with forward and reverse deltas
The PatchType indicates which of these flavors a given FileHeader
is looking at. Right now we assume UNIFIED by default as that is
the most common form used.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>