pgsql: Fix grammar for IN/OUT/INOUT parameters.

Log Message:
-----------
Fix grammar for IN/OUT/INOUT parameters. This commit doesn't actually
implement any new feature, it just pushes the 'not implemented' error
message deeper into the backend. I also tweaked the grammar to accept
Oracle-ish parameter syntax (parameter name first), as well as the
SQL99 standard syntax (parameter mode first), since it was easy and
people will doubtless try to use both anyway.

Modified Files:
--------------
pgsql/src/backend/commands:
functioncmds.c (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/functioncmds.c.diff?r1=1.57&r2=1.58)
pgsql/src/backend/nodes:
copyfuncs.c (r1.298 -> r1.299)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c.diff?r1=1.298&r2=1.299)
equalfuncs.c (r1.237 -> r1.238)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c.diff?r1=1.237&r2=1.238)
pgsql/src/backend/parser:
gram.y (r2.484 -> r2.485)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.484&r2=2.485)
pgsql/src/include/nodes:
parsenodes.h (r1.274 -> r1.275)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h.diff?r1=1.274&r2=1.275)