Deathcam Update #2

Okay gents, here is a rundown of things fixed for THIS patch!

-When deathcam was active, the "Press ... to accept your fate" message at the top was flickering. There was a refresh in draw_ter() that was emptying the curses buffer, and I slipped in a mvwprintz() to there as well so it doesn't flicker.

-The hang described by @Rivet-the-Zombie & @KA101 was due to show_once not being changed (resulting in an always true while() loop, no fun). The latency issue described by @kevingranade was due to some weird mishap with a blocking read call as far as I can tell (press key once in deathcam, animation and actions suspend, press again, and it reads it). Not really sure why it was happening that way, but I reverted the logic for handle_mouseview back to 'return true' instead of 'return !u.is_dead_state()' and a few other things, and it seems to have fixed it.

Cthulhu only knows if I forgot something else, but if I did, you guys have been great at pointing it out! :-)

Hope this helps mateys!
-Davek