9term: set TERM=dumb instead of TERM=9term

Everyone seems to assume that TERM != dumb implies
ANSI escape codes are okay. In fact, many people assume
that unconditionally, but it is easier to argue back about
TERM=dumb than TERM=9term.

This applies to acme win too, because they share the code.

Set termprog=9term or termprog=win for clients who
need to know.

R=rsc
CC=r
https://codereview.appspot.com/12532043
4 files changed