You're never gonna be right 100% of the time when guessing how much buffer
space you need. This avoids having to make that type of decision in a bunch
of cases. :^)
You can now open as many PTY pairs as you like. Well, it's actually capped
at 8 for now, but it's just a constant and trivial to change.
Unregistering a PTY pair is untested because I didn't want to start
mucking with that in Terminal right now.
