terminal.c's from_backend() no longer calls term_out(), because

terminal.c's from_backend() no longer calls term_out(), because
term_out() can in turn call ldisc_send() which calls back to
from_backend() when local echo is enabled. This was giving rise to
crazy re-entrancy stuff and stack overflows. Instead from_backend()
deposits its data in a bufchain which term_out() empties the next
time it's called.

[originally from svn r1276]