3335 - bugfix

After all that, update_optimized_body was again failing on '+'!

This fix adds two more blemishes to my inventory of 3331: the new
version is no longer shorter, and there's now a second correct_args
temporary.

I'm still assuming that the param is a rest param if the args are a
cons. Can I get away with that?
3336 - nooo, macex is still all fucked up

Multiary map test failing.

I was incorrectly assuming that is_macro implied in_macro(). But even
fixing that isn't the key difference between the macex and genuine-list-arg-for-quoted-param
scenarios.
3337 - omg, tests pass and + has an optimized_body

I don't feel sure so far, but it seems the solution is to strip all ''
for args of quoted rest params in non-macros. Phew.

Code is butt-ugly with -- count them -- three boolean params.
3338 - cleanup
3339

Optimization: minimize consing.