pgsql: Cast slightly abused enum to int, so that GCC 4.5 won't warn

Log Message:
-----------
Cast slightly abused enum to int, so that GCC 4.5 won't warn about switch
cases that are not part of the enum's definition.

Modified Files:
--------------
pgsql/src/backend/nodes:
read.c (r1.53 -> r1.54)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/read.c?r1=1.53&r2=1.54)