pillowfight: include errno.h

Change-Id: Ieb3ed381295d3ad7cf3c35dc55715f22d634bd24
Reviewed-on: http://review.couchbase.org/41995
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>