A bug in the command line argument parsing code was making
pickaxe not to work at all in diff-cache and diff-files commands.
Embarrassingly enough, the working pickaxe in diff-tree tells me
that it was not working in these two commands from day one.
This patch fixes it.

Also updates the documentation to describe the --pickaxe-all option.
Signed-off-by: NJunio C Hamano <junkio@cox.net>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>