core: add --stream-capture

This is a partial revert of commit 7059c15, and basically re-adds
--capture, just with different option names and slightly different
semantics.
core: re-add -dumpstream as --stream-dump

Apparently useful for dumping DVD. Could also be used to rip streams
with libquvi and such, but for that there are better tools. Actually
I doubt there aren't better tools to dump DVDs, but whatever, this was
a feature request, so I don't need a good reason.
ao_coreaudio: fix switched parameters