git-repack --max-pack-size: write_{object,one}() respect pack limit

git-repack --max-pack-size: write_{object,one}() respect pack limit

With --max-pack-size,  generate the appropriate write limit
for each object and check against it before each group of writes.
Update delta usability rules to handle base being in a previously-
written pack.  Inline sha1write_compress() so we know the
exact size of the written data when it needs to be compressed.
Detect and return write "failure".

Signed-off-by: Dana L. How <danahow@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>