[PATCH] diff: consolidate various calls into diffcore.

[PATCH] diff: consolidate various calls into diffcore.

The three diff-* brothers had a sequence of calls into diffcore
that were almost identical.  Introduce a new diffcore_std()
function that takes all the necessary arguments to consolidate
it.  This will make later enhancements and changing the order of
diffcore application simpler.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>