Rethinking pg_dump's function sorting code

In bug #12832 Marko Tiikkaja points out that commit
7b583b20b1c95acb621c71251150beef958bb603 created a rather unnecessary
dump failure hazard, since it applies pg_get_function_identity_arguments()
to every function in the database, even those that won't get dumped.
I think we should fix this by getting rid of pg_dump's use of that
function altogether. A low-tech way to sort functions of identical names
would be to compare argument type OIDs, as in the attached simple patch.
If people feel it's important to avoid depending on numerical OID order,
we could instead look up type names locally and compare them as in the
attached less-simple patch. (Both patches neglect reverting the data
collection aspects of the prior commit, since that's mechanical; the only
interesting part is what we'll do to sort.)

Neither patch will exactly preserve the sort behavior of the current
code, but I don't think that's important.

Comments?

regards, tom lane