BUG #2073: Can't drop sequence when created via SERIAL column

The following bug has been logged online:

Bug reference:      2073
Logged by:          Aaron Dummer
Email address:      aaron@dummer.info
PostgreSQL version: 8.0.3
Operating system:   Debian Linux
Description:        Can't drop sequence when created via SERIAL column
Details:

If I create a table named foo with a column named bar, column type SERIAL,
it auto-generates a sequence named foo_bar_seq.  Now if I manually create a
new sequence called custom_seq, and change the default value of foo.bar to
reference the new sequence, I still can't delete the old sequence
(foo_bar_seq).

In other words, from a user's point of view, the foo table is no longer
dependent on the foo_bar_seq, yet the system still sees it as dependent.

I brought this topic up on the #postgresql IRC channel and the behavior was
confirmed by AndrewSN, scampbell_, and mastermind.