rgw: avoid sighandler_t in favor of sig_t

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
rgw: add compat file for name service macros

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
Merge pull request #822 from ceph/port/rgw

portability patches in rgw 

Reviewed-by: Sage Weil <sage@inktank.com>