win terminal doesn't track mouse wheel?

[sfeam (E. Merritt) <eam...@gm...>]

It seems that the zoom/pan response to scrolling the mouse wheel,
added by James Van Zandt in 2009, is not working in the windows
terminal.  Is this correct?  

I think the only thing missing is that  it needs to pass through 
WM_MOUSEWHEEL events from WndGraphProc() in wgraph.c.  Currently
it passes through events triggered by WM_LBUTTONUP, WM_LBUTTONDOWN,
etc, but not WM_MOUSEWHEEL.

The main mousing code wants to see this as a GP_buttonpress event,
with parameter
  4 = mouse wheel scrolled up
  5 = mouse wheel scrolled down
and the shift/control/alt modifiers filled in as usual.

Any volunteers to look into adding that?

	Ethan