Merge in numerous local fixes: - when outputing character to the screen check
that we actually have a character for the charcode supplied. This fixes
potential segfault when user types in some character that isn't in the
table; - don't hog all CPU time when playing level completion sound. This also
makes level completion sound much more less jerky; - by default use sdl12
library instead of sdl10, because sdl10 is at the end of its lifecycle and
would be retired RSN.