[gk] Increase print buffer, add size check

[water111]

This should fix the crash when entering the freedom HQ elevator. It was caused by a large number of prints, one for each process in the city being killed by check-for-rougue-process, which would overflow the print buffer. So I increased the print buffer.

Detecting buffer overflow here is hard because lots of things are allowed to write to it, including the user's GOAL print methods. I added a basic check that will assert when there's 1k or less space in the buffer. It won't catch every overflow, but it would have caught this one.