BUG #6212: PREPARE(pseudotype) should be blocked off

The following bug has been logged online:

Bug reference:      6212
Logged by:          Caleb Welton
Email address:      Caleb.Welton@emc.com
PostgreSQL version: 9.0
Operating system:   OSX
Description:        PREPARE(pseudotype) should be blocked off
Details:

statements such as:
  PREPARE p1(anyelement) AS SELECT quote_literal($1);
  PREPARE p2(internal) AS SELECT int2recv($1);

Should not be allowed.

They can result in peculiar behavior such as the following:

execute p1('hello')
ERROR:  cannot display a value of type anyelement