pgsql: Add a paramtypmod field to Param nodes.

Log Message:
-----------
Add a paramtypmod field to Param nodes. This is dead weight for Params
representing externally-supplied values, since the APIs that carry such
values only specify type not typmod. However, for PARAM_SUBLINK Params
it is handy to carry the typmod of the sublink's output column. This
is a much cleaner solution for the recently reported 'could not find
pathkey item to sort' and 'failed to find unique expression in subplan
tlist' bugs than my original 8.2-compatible patch. Besides, someday we
might want to support typmods for external parameters ...

Modified Files:
--------------
pgsql/src/backend/nodes:
copyfuncs.c (r1.353 -> r1.354)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/copyfuncs.c.diff?r1=1.353&r2=1.354)
equalfuncs.c (r1.287 -> r1.288)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/equalfuncs.c.diff?r1=1.287&r2=1.288)
outfuncs.c (r1.285 -> r1.286)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c.diff?r1=1.285&r2=1.286)
readfuncs.c (r1.195 -> r1.196)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/readfuncs.c.diff?r1=1.195&r2=1.196)
pgsql/src/backend/optimizer/plan:
subselect.c (r1.113 -> r1.114)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/subselect.c.diff?r1=1.113&r2=1.114)
pgsql/src/backend/parser:
parse_agg.c (r1.73 -> r1.74)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_agg.c.diff?r1=1.73&r2=1.74)
parse_coerce.c (r2.146 -> r2.147)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_coerce.c.diff?r1=2.146&r2=2.147)
parse_expr.c (r1.198 -> r1.199)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_expr.c.diff?r1=1.198&r2=1.199)
pgsql/src/include/catalog:
catversion.h (r1.361 -> r1.362)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.361&r2=1.362)
pgsql/src/include/nodes:
primnodes.h (r1.117 -> r1.118)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/primnodes.h.diff?r1=1.117&r2=1.118)