zoomRectangle pixel input is confusing

[sdlime]

Folks: The pixel input is confusing for zoomRectangle. A rectangle is minx,
miny, maxx, maxy and the code should take care of dealing with orientation
issues (e.g. images have UL origin, maps LL origin) as opposed to the user. It's
confusing, at least to me, to specify a rectangle with maxy <= miny. See bugs
1982 and 1817 for instances where this has tripped us up in the past.

With 5.0 I think we should support a proper rect as input, and allow flipped y
coordinates for backwards compatability.

Steve