add an optional tty window for the inferior

[tromey]

Let the user make a tty window for the inferior.

[tromey]

There's not really good way to do this at the moment. We can't easily run the inferior using the tty. Nor can we get the name of the slave side of the pty from VTE. It could be done perhaps if we can call ptsname, perhaps using ctypes. Or, lobby for an addition to VTE. Then we could fork the tty using some null program, then set the gdb tty

[o11c]

I've done this by spawning an xterm (with or without -S), but I still had.

Some WIP for the -S method: https://gist.github.com/o11c/1780b2f1b2729f335787