object name of pre- and post-image blob on the "index"
line when generating a patch format output.
+--abbrev::
+ Instead of showing the full 40-byte hexadecimal object
+ name in diff-raw format output and diff-tree header
+ lines, show only handful prefix. This is independent of
+ --full-index option above, which controls the diff-patch
+ output format.
+
-B::
Break complete rewrite changes into pairs of delete and create.