pgsql: Arrange for an explicit cast applied to an ARRAY[] constructor to

Log Message:
-----------
Arrange for an explicit cast applied to an ARRAY[] constructor to be applied
directly to all the member expressions, instead of the previous implementation
where the ARRAY[] constructor would infer a common element type and then we'd
coerce the finished array after the fact. This has a number of benefits,
one being that we can allow an empty ARRAY[] construct so long as its
element type is specified by such a cast.

Brendan Jurd, minor fixes by me.

Modified Files:
--------------
pgsql/doc/src/sgml:
syntax.sgml (r1.121 -> r1.122)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/syntax.sgml?r1=1.121&r2=1.122)
pgsql/src/backend/nodes:
copyfuncs.c (r1.388 -> r1.389)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c?r1=1.388&r2=1.389)
equalfuncs.c (r1.318 -> r1.319)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c?r1=1.318&r2=1.319)
outfuncs.c (r1.322 -> r1.323)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.322&r2=1.323)
pgsql/src/backend/parser:
gram.y (r2.608 -> r2.609)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y?r1=2.608&r2=2.609)
parse_expr.c (r1.226 -> r1.227)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_expr.c?r1=1.226&r2=1.227)
parse_target.c (r1.158 -> r1.159)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_target.c?r1=1.158&r2=1.159)
pgsql/src/include/nodes:
nodes.h (r1.205 -> r1.206)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/nodes.h?r1=1.205&r2=1.206)
parsenodes.h (r1.359 -> r1.360)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h?r1=1.359&r2=1.360)
pgsql/src/test/regress/expected:
arrays.out (r1.34 -> r1.35)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/arrays.out?r1=1.34&r2=1.35)
pgsql/src/test/regress/sql:
arrays.sql (r1.26 -> r1.27)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/arrays.sql?r1=1.26&r2=1.27)