Fix getting function arguments so it's repeatable.

Getting the args would only work once.  The key was SP = MARK after av_make().
I failed to crib that from pp_anonlist().  I guess that was leaving the stack
in a weird state, or the mark... not sure.

I also made sure to POPs the return value from call_method() before PUTBACK
to better emulate what's in perlcall.

Added some tests to make sure we can get the args more than once.