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

src/cmd/9term/rcstart.c

@@ -77,7 +77,16 @@ rcstart(int argc, char **argv, int *pfd, int *tfd)
 	 */
 	notifyoff("sys: window size change");
 
-	putenv("TERM", "9term");
+	// This used to be TERM=9term but we don't know of anything that cares.
+	// Worse, various cc have started assuming that TERM != dumb implies
+	// the ability to understand ANSI escape codes. 9term will squelch them
+	// but acme win does not.
+	putenv("TERM", "dumb");
+
+	// Set $termprog to 9term or win for those who care about what kind of
+	// dumb terminal this is.
+	putenv("termprog", (char*)termprog);
+
 	pid = fork();
 	switch(pid){
 	case 0: