pgsql: Get rid of the SpinLockAcquire/SpinLockAcquire_NoHoldoff

Log Message:
-----------
Get rid of the SpinLockAcquire/SpinLockAcquire_NoHoldoff distinction
in favor of having just one set of macros that don't do HOLD/RESUME_INTERRUPTS
(hence, these correspond to the old SpinLockAcquire_NoHoldoff case).
Given our coding rules for spinlock use, there is no reason to allow
CHECK_FOR_INTERRUPTS to be done while holding a spinlock, and also there
is no situation where ImmediateInterruptOK will be true while holding a
spinlock. Therefore doing HOLD/RESUME_INTERRUPTS while taking/releasing a
spinlock is just a waste of cycles. Qingqing Zhou and Tom Lane.

Modified Files:
--------------
pgsql/src/backend/access/transam:
xlog.c (r1.224 -> r1.225)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c.diff?r1=1.224&r2=1.225)
pgsql/src/backend/storage/buffer:
bufmgr.c (r1.200 -> r1.201)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/bufmgr.c.diff?r1=1.200&r2=1.201)
pgsql/src/backend/storage/ipc:
shmem.c (r1.88 -> r1.89)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/shmem.c.diff?r1=1.88&r2=1.89)
pgsql/src/backend/storage/lmgr:
lwlock.c (r1.36 -> r1.37)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lwlock.c.diff?r1=1.36&r2=1.37)
pgsql/src/include/storage:
buf_internals.h (r1.83 -> r1.84)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/buf_internals.h.diff?r1=1.83&r2=1.84)
spin.h (r1.26 -> r1.27)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/spin.h.diff?r1=1.26&r2=1.27)