pgsql: Revise hash join code so that we can increase the number of

Log Message:
-----------
Revise hash join code so that we can increase the number of batches
on-the-fly, and thereby avoid blowing out memory when the planner has
underestimated the hash table size. Hash join will now obey the
work_mem limit with some faithfulness. Per my recent proposal
(hash aggregate part isn't done yet though).

Modified Files:
--------------
pgsql/src/backend/executor:
nodeHash.c (r1.88 -> r1.89)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeHash.c.diff?r1=1.88&r2=1.89)
nodeHashjoin.c (r1.67 -> r1.68)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeHashjoin.c.diff?r1=1.67&r2=1.68)
pgsql/src/backend/optimizer/path:
costsize.c (r1.137 -> r1.138)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/costsize.c.diff?r1=1.137&r2=1.138)
pgsql/src/backend/utils/adt:
selfuncs.c (r1.171 -> r1.172)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c.diff?r1=1.171&r2=1.172)
pgsql/src/include/executor:
hashjoin.h (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/hashjoin.h.diff?r1=1.34&r2=1.35)
nodeHash.h (r1.35 -> r1.36)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/nodeHash.h.diff?r1=1.35&r2=1.36)
nodeHashjoin.h (r1.28 -> r1.29)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/nodeHashjoin.h.diff?r1=1.28&r2=1.29)
pgsql/src/include/nodes:
execnodes.h (r1.122 -> r1.123)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/execnodes.h.diff?r1=1.122&r2=1.123)
pgsql/src/include/utils:
selfuncs.h (r1.21 -> r1.22)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/selfuncs.h.diff?r1=1.21&r2=1.22)