pack-bitmaps: plug memory leak, fix allocation size for recent_bitmaps
pack-bitmaps: plug memory leak, fix allocation size for recent_bitmaps

Use an automatic variable for recent_bitmaps, an array of pointers.
This way we don't allocate too much and don't have to free the memory
at the end.  The old code over-allocated because it reserved enough
memory to store all of the structs it is only pointing to and never
freed it.  160 64-bit pointers take up 1280 bytes, which is not too
much to be placed on the stack.

MAX_XOR_OFFSET is turned into a preprocessor constant to make it
constant enough for use in an non-variable array declaration.

Noticed-by: Stefan Beller <42740f1721ea98c94a07c13b76c86023ff11da2d@gmail.com>
Suggested-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>
Signed-off-by: Rene Scharfe <2da278a99b557fc93ddbed7517a413ad793e2e6a@web.de>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

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