Sync OpenBSD patchset 642:

Add an option to disable the smcup/rmcup alternate screen behaviour inside
tmux. From clemens fischer.

tmux.1

@@ -1,4 +1,4 @@
-.\" $Id: tmux.1,v 1.231 2010-02-08 18:31:07 tcunha Exp $
+.\" $Id: tmux.1,v 1.232 2010-02-08 18:32:34 tcunha Exp $
 .\"
 .\" Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
 .\"
@@ -14,7 +14,7 @@
 .\" IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 .\" OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: February 7 2010 $
+.Dd $Mdocdate: February 8 2010 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -1898,6 +1898,19 @@ command.
 Duplicate input to any pane to all other panes in the same window, except
 for panes that are not in output mode.
 .Pp
+.It Xo Ic alternate-screen
+.Op Ic on | off
+.Xc
+This option configures whether programs running inside
+.Nm
+may use the terminal alternate screen feature, which allows the
+.Em smcup
+and
+.Em rmcup
+.Xr terminfo 5
+capabilities to be issued to preserve the existing window content on start and
+restore it on exit.
+.Pp
 .It Xo Ic utf8
 .Op Ic on | off
 .Xc