[PATCH] Tweak diffcore-rename heuristics.

[PATCH] Tweak diffcore-rename heuristics.

The heuristics so far was to compare file size change and xdelta
size against the average of file size before and after the
change.  This patch uses the smaller of pre- and post- change
file size instead.

It also makes a very small performance fix.  I didn't measure
it; I do not expect it to make any practical difference, but
while scanning an already sorted list, breaking out in the
middle is the right thing.

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