[PATCH 19/21] [terminal] guard open and close against repeated calls

[Ray Strode]

Hi,

> I thought about that; but one advantage of just making them guards is
> that then the renderers and plugins don't have to care.
>
> They can just call ply_terminal_open() on the terminal, without first
> checking the is_open -- which makes it much more "I need this terminal
> open, open it if it isn't" -- and I kinda like that.
Alright, sounds fine then.  It would probably be a good idea to have a
ply_trace in those cases just so we can identify when it happens when
debugging.

--Ray