Allow CREATE OR REPLACE VIEW to rename the columns

Hi,

Currently CREATE OR REPLACE VIEW command fails if the column names
are changed. For example,

    =# CREATE VIEW test AS SELECT 0 AS a;
    =# CREATE OR REPLACE VIEW test AS SELECT 0 AS x;
    ERROR:  cannot change name of view column "a" to "x"

I'd like to propose the attached patch that allows CREATE OR REPLACE VIEW
to rename the view columns. Thought?

Regards,

-- 
Fujii Masao