Remove tui-out.[ch]

The other day on irc, we were discussing the "m_line" hack in
tui-out.c, and I mentioned that it would be nice to replace this with
a new ui_out_flag.

Later, I looked at ui_out_flag and found:

      ui_source_list = (1 << 0),

... and sure enough, this is tested already.

This patch removes tui-out.[ch] and changes the TUI to use an ordinary
cli-out object without this flag set.

As far as I can tell, this doesn't affect behavior at all -- the TUI
tests all pass, and interactively I tried switching stack frames,
"list", etc, and it all seems to work.

New in v2: fixed the problem pointed out by Keith, and added a test
case for that scenario.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>