Log Message:
-----------
Hyperlink a reference to DROP CAST in the CREATE CAST reference page.
Modified Files:
--------------
pgsql-server/doc/src/sgml/ref:
create_cast.sgml (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/ref/create_cast.sgml.diff?r1=1.17&r2=1.18)