[GRASS5] gis.m: Zoom and region overhaul, bindings

[Cedric Shock]

Hey,

I tossed some more changes to mapcanvas.tcl the CVS direction.

I eliminated almost all of the usage of g.region in mapcanvas.tcl. It is now 
used for the following:
1. Saving the current region as gism_temp_region before rendering
2. Setting the region to match the zoom before rendering
2. Loading gism_temp_region after rendering to get the current region back
4. Getting zoom boxes from the current region / default region / saved 
regions.

There is no longer any need for the mon_* regions (they are no longer made).

The region previous_zoom is no longer used. Previous zooms are now independent 
of each other on each display.

The bounds for zooming and panning are stored in a mapcanvas variable 
"moitor_zooms" instead of in regions. There is a history of previous zooms. 
It is currently set to 7 (arbitrary).

The background changed region affecting rendering bug is gone.

I cleaned up and greatly simplified the bindings for switching trees in the 
gis.m main window. Clicking on windows or "alt-tabbing" to them now brings up 
their tree in the gis.m main window.

--Cedric