Fix prompt character input

[mehalter]

When using the prompts, the behavior is not correct. If it prompts me to update PATH, I have to type n and then a carriage return to trigger the read to finish. It then reads a character, n and on the second prompt asking to update FPATH, the read already has another character to read which is the \n to finish the previous read. This means to deny the second prompt you must preemptively type nn\n on the first question. This changes the tty mode so that it reads the raw character input, prompts, reads a single character, and puts the tty mode back. This fixes this bug and also makes it so you don't have to press return on prompts.

[mehalter]

I'm not super happy with this implementation, but I'm not sure how else to fix this bug in Julia.

[Roger-luo]

nice, this was indeed not correct behavior. I guess I didn't test the deny behavior much (actually I'm not sure how to test these shell commands at all) but I'll merge this first.