pgsql: More fixes for 8.4 DTrace probes.

Log Message:
-----------
More fixes for 8.4 DTrace probes.  Remove useless BUFFER_HIT/BUFFER_MISS
probes --- the BUFFER_READ_DONE probe provides the same information and more
besides.  Expand the LOCK_WAIT_START/DONE probe arguments so that there's
actually some chance of telling what is being waited for.  Update and
clean up the documentation.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        installation.sgml (r1.319 -> r1.320)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml?r1=1.319&r2=1.320)
        monitoring.sgml (r1.64 -> r1.65)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/monitoring.sgml?r1=1.64&r2=1.65)
    pgsql/src/backend/storage/buffer:
        bufmgr.c (r1.248 -> r1.249)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/bufmgr.c?r1=1.248&r2=1.249)
    pgsql/src/backend/storage/lmgr:
        lock.c (r1.186 -> r1.187)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lock.c?r1=1.186&r2=1.187)
    pgsql/src/backend/utils:
        probes.d (r1.8 -> r1.9)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/probes.d?r1=1.8&r2=1.9)