Do not grab the synaptics device if not running on the current VT.
This helps when switching user or more in general when running more than one
instance of Xorg.

Index: xserver-xorg-input-synaptics/src/synaptics.c
===================================================================
--- xserver-xorg-input-synaptics.orig/src/synaptics.c	2009-11-19 21:14:09.183725703 +0900
+++ xserver-xorg-input-synaptics/src/synaptics.c	2009-11-19 22:00:51.296245013 +0900
@@ -747,6 +747,9 @@
 
     DBG(3, ErrorF("Synaptics DeviceOn called\n"));
 
+    if (xf86Screens[0]->vtSema == FALSE)
+	    return !Success;
+
     SetDeviceAndProtocol(local);
     local->fd = xf86OpenSerial(local->options);
     if (local->fd == -1) {