Fix hash function in xdiff library
Fix hash function in xdiff library

Jim Mayering noticed that xdiff library took insanely long time
when comparing files with many identical lines.

This was because the hash function used in the library is broken
on 64-bit architectures and caused too many collisions.

http://thread.gmane.org/gmane.comp.version-control.git/28962/focus=28994

Acked-by: Davide Libenzi <91df8000b8dca80eb036dde93edf593d4a91414e@xmaliserver.org>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git