pgsql-server: Improve spinlock selftest to make it able to detect

Log Message:
-----------
Improve spinlock selftest to make it able to detect misdeclaration of
the slock_t datatype (ie, declared type smaller than what the hardware
TAS instruction needs).

Modified Files:
--------------
pgsql-server/src/backend/storage/lmgr:
s_lock.c (r1.31 -> r1.32)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/lmgr/s_lock.c.diff?r1=1.31&r2=1.32)