pgsql: Now that we've rearranged relation open to get a lock before

Log Message:
-----------
Now that we've rearranged relation open to get a lock before touching
the rel, it's easy to get rid of the narrow race-condition window that
used to exist in VACUUM and CLUSTER. Did some minor code-beautification
work in the same area, too.

Modified Files:
--------------
pgsql/src/backend/access/heap:
heapam.c (r1.218 -> r1.219)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c.diff?r1=1.218&r2=1.219)
pgsql/src/backend/commands:
analyze.c (r1.96 -> r1.97)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/analyze.c.diff?r1=1.96&r2=1.97)
cluster.c (r1.152 -> r1.153)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/cluster.c.diff?r1=1.152&r2=1.153)
lockcmds.c (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/lockcmds.c.diff?r1=1.14&r2=1.15)
vacuum.c (r1.337 -> r1.338)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c.diff?r1=1.337&r2=1.338)
pgsql/src/backend/storage/lmgr:
lmgr.c (r1.86 -> r1.87)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lmgr.c.diff?r1=1.86&r2=1.87)
pgsql/src/include/access:
heapam.h (r1.114 -> r1.115)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/heapam.h.diff?r1=1.114&r2=1.115)
pgsql/src/include/storage:
lmgr.h (r1.55 -> r1.56)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lmgr.h.diff?r1=1.55&r2=1.56)