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). I am almost certain this was due to the change I made in handle_mouseview using 'return !u.is_dead_state()' instead of 'return true'. Upon changing it back, it seems to have disappeared.

-Since the reversion back to return true in handle_mouseview, show_once seems to not work all that well, so I have instead opted for a simple break in the event of deathcam.

Latest build (Linux ncurses) works fine as far as I can see, but Cthulhu only knows if I forgot something else. If I did, you guys have been great at pointing it out! :-)

Hope this helps mateys!
-Davek