9term, acme: autoscroll

Ignore scroll/noscroll window setting.
Instead, scroll when the write begins in
or immediately after the displayed window content.

In the new scrolling discipline, executing
"Noscroll" is replaced by typing Page Up or
using the mouse to scroll higher in the buffer,
and executing "Scroll" is replaced by typing End
or using the mouse to scroll to the bottom of
the buffer.

R=r, r2
http://codereview.appspot.com/4433060

man/man1/9term.1

@@ -30,8 +30,9 @@ Otherwise button 2 brings up a menu, described below.
 .PP
 The
 .B -s
-option initializes the window so that text scrolls;
-the default is not to scroll.
+option has no effect.  It formerly set the scrolling mode,
+and is recognized to avoid breaking scripts that create new windows.
+See below for a description of scrolling behavior.
 .PP
 The
 .B -c
@@ -205,10 +206,9 @@ always treats the DEL keystroke as an interrupt request.
 In response it sends the terminal's current interrupt character
 (which need not be DEL).
 .PP
-Normally, written output to a window blocks when
-the text reaches the end of the screen and the terminal
-buffer fills;
-a button 2 menu item toggles scrolling.
+Written output to a window is appended to the end of the window.
+The window scrolls to display the new output only if the
+end of the window was visible before the write.
 .PP
 .I 9term
 changes behavior according to