Try to determine if we are operating on a system with dual monitors.  It even handles switching modes mid-execution.  At least on Windows.  The maxsize command seems to keep up with the changes to the display. [Damon Courtney]

 proc DualMonitors {} {
     set top .#dualMonitorCheck#
     if {![winfo exists $top]} { toplevel $top; wm withdraw $top }
     set sw [winfo screenwidth $top]
     set mw [lindex [wm maxsize .] 0]
     return [expr {($sw * 2) < $mw}]
 }

----

This doesn't work when running wish on MacOSX with X11. I've got dual monitors but the proc returns 0. For
my setup, the value for sw is 2624 (1600 + 1024) and the value of mw is (curiously) 2609.