pgsql: Code review for CREATE OR REPLACE VIEW patch.

Log Message:
-----------
Code review for CREATE OR REPLACE VIEW patch.  Do things in a saner order to
result in hopefully-less-confusing error messages when the new definition
isn't compatible with the old; minor other cleanup.

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        create_view.sgml (r1.38 -> r1.39)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_view.sgml?r1=1.38&r2=1.39)
    pgsql/src/backend/commands:
        tablecmds.c (r1.273 -> r1.274)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/tablecmds.c?r1=1.273&r2=1.274)
        view.c (r1.108 -> r1.109)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/view.c?r1=1.108&r2=1.109)
    pgsql/src/test/regress/expected:
        create_view.out (r1.14 -> r1.15)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/create_view.out?r1=1.14&r2=1.15)