Move functions from cache.h for zlib.c into a new header file. Since
adding a "zlib.h" would cause issues with the real zlib, rename zlib.c
to git-zlib.c while we are at it.
Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
