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)