[openbox] Weird bug with NextWindow (ALT+TAB)

[Danko Krajisnik]

As it turns out, Xmodmap is the cause of the problem! If I use A-Tab 
instead of W-Tab (and don't run xmodmap), it works fine.  However, I use 
an IBM Model M keyboard so there is no Win key. I map the left Alt to a 
Win key so that Openbox keybindings dont interfere with other programs. 
How can I use xkb to remap the left Alt to a Win key? This is 2 lines in 
my .Xmodmap file but it looks to be more confusing with xkb.

Thanks!