Fix segmentation fault in mbsdiff and fix crc by linking with libbz2.

Fix segmentation fault in mbsdiff and fix crc by linking with libbz2.

Doh! I typed memcpy when I really wanted memset.

This does not actually introduce any new dependencies.  Evergreen
updates/installation already requires bzip2.  If bzip2 is present,
then libbz2 is present.  We don't need libbz2 headers, just the
library itself for a single data structure used in crc32 calculation.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>