pgsql: Make plpgsql support FOR over a query specified by a cursor

Log Message:
-----------
Make plpgsql support FOR over a query specified by a cursor declaration,
for improved compatibility with Oracle.

Pavel Stehule, with some fixes by me.

Modified Files:
--------------
pgsql/doc/src/sgml:
plpgsql.sgml (r1.126 -> r1.127)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/plpgsql.sgml?r1=1.126&r2=1.127)
pgsql/src/pl/plpgsql/src:
gram.y (r1.109 -> r1.110)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/gram.y?r1=1.109&r2=1.110)
pl_comp.c (r1.123 -> r1.124)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_comp.c?r1=1.123&r2=1.124)
pl_exec.c (r1.208 -> r1.209)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_exec.c?r1=1.208&r2=1.209)
pl_funcs.c (r1.68 -> r1.69)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_funcs.c?r1=1.68&r2=1.69)
plpgsql.h (r1.96 -> r1.97)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/plpgsql.h?r1=1.96&r2=1.97)
pgsql/src/test/regress/expected:
plpgsql.out (r1.60 -> r1.61)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/plpgsql.out?r1=1.60&r2=1.61)
pgsql/src/test/regress/sql:
plpgsql.sql (r1.50 -> r1.51)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/plpgsql.sql?r1=1.50&r2=1.51)