This is a halfway between debugging aid and a helper to write an
ultra-smart merge scripts.  The new option takes a string that
consists of a list of "status" letters, and limits the diff
output to only those classes of changes, with two exceptions:

 - A broken pair (aka "complete rewrite"), does not match D
   (deleted) or N (created).  Use B to look for them.

 - The letter "A" in the diff-filter string does not match
   anything itself, but causes the entire diff that contains
   selected patches to be output (this behaviour is similar to
   that of --pickaxe-all for the -S option).

For example,

    $ git-rev-list HEAD |
      git-diff-tree --stdin -s -v -B -C --diff-filter=BCR

shows a list of commits that have complete rewrite, copy, or
rename.
Signed-off-by: NJunio C Hamano <junkio@cox.net>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>