poorly written builtin functions

I'm working on writing a script that automatically tests all the
built-in functions. As a first step, I just passed NULL for all
of the arguments for each built-in function. I've attached a
list of the 90 functions that crash the backend when this is done.

Since the culprit functions all seem related (I believe they're
all generated by src/backend/utils/mb/conversion_procs), I'd
imagine this should be pretty easy to fix. I haven't played
with this part of the backend before, so if someone else would
like to make the necessary changes, let me know. Otherwise
I'll do it.

As for the testing script itself, it's not finished (testing
NULL inputs is just a trivial first step); when it's done, I'll
submit it for inclusion in CVS.

-Neil