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.

git-svn-id: svn://svn.tartarus.org/sgt/putty@1276 cda61777-01e9-0310-a592-d414129be87e