BUG #6363: pgp_sym_encrypt() broken between 8.4 and 9.1

The following bug has been logged on the website:

Bug reference: 6363
Logged by: Dean Schulze
Email address: dean(dot)w(dot)schulze(at)gmail(dot)com
PostgreSQL version: 9.1.1
Operating system: Windows 7 Pro 64-bit
Description:

The following worked in 8.4, but fails in 9.1. (pgpcrypto is installed.)

In 9.1 it looks like it doesn't recognize strings.

insert into credentials values('demo', pgp_sym_encrypt('password',
'longpassword'));

ERROR: function pgp_sym_encrypt(unknown, unknown) does not exist
LINE 1: insert into credentials values('demo', pgp_sym_encrypt('pass...
^
HINT: No function matches the given name and argument types. You might need
to add explicit type casts.

********** Error **********

ERROR: function pgp_sym_encrypt(unknown, unknown) does not exist
SQL state: 42883
Hint: No function matches the given name and argument types. You might need
to add explicit type casts.
Character: 40