buffer: uninline, constify crc32c()

Signed-off-by: Sage Weil <sage@inktank.com>
common: fix Mutex, Cond no-copy declarations

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #591 from ceph/wip-misc

Reviewed-by: Greg Farnum <greg@inktank.com>