pactest: create packages in memory

pactest: create packages in memory

This is similar to what was just done for the sync databases. Move a few
pieces around so we never need to actually write out the filesystem to
create a package, and simply stream the tarfile out from the data we've
collected.

Once again, a few newline addition hacks and other things have to be
left in place in order not to break everything; this time however most
of the assumptions are in pactest and not libalpm.

Signed-off-by: Dan McGee <dan@archlinux.org>