pgsql: There is no need for ReadBuffer() call sites to check that the

Log Message:
-----------
There is no need for ReadBuffer() call sites to check that the returned
buffer is valid, as ReadBuffer() will elog on error. Most of the call
sites of ReadBuffer() got this right, but this patch fixes those call
sites that did not.

Modified Files:
--------------
    pgsql/src/backend/access/heap:
        heapam.c (r1.180 -> r1.181)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c.diff?r1=1.180&r2=1.181)
    pgsql/src/backend/commands:
        analyze.c (r1.78 -> r1.79)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/analyze.c.diff?r1=1.78&r2=1.79)
        sequence.c (r1.117 -> r1.118)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/sequence.c.diff?r1=1.117&r2=1.118)
        trigger.c (r1.174 -> r1.175)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c.diff?r1=1.174&r2=1.175)