Use target_terminal_ours_for_output in warning/internal_error

Use target_terminal_ours_for_output in warning/internal_error

We're only doing output here, so leave raw/cooked mode alone, as well
as the SIGINT handler.

And restore terminal settings, while at it.

gdb/ChangeLog:
2016-04-12  Pedro Alves  <palves@redhat.com>

	* utils.c (vwarning, internal_vproblem): Use
	make_cleanup_restore_target_terminal and
	target_terminal_ours_for_output.