Adds maxZoomLevel option for WFS layer

[fvanderbiest]

This patch adds the ability to load a WFS layer only between some zoom levels. Should be generalized to other types of layer ?

[fvanderbiest]

wfs maxZoomLevel

[crschmidt]

The right way to do this is to use scale based rendering -- maxRes/minRes options on the layer, rather than min/max zoom level. (the existing minzoomlevel support was a hack that should have been removed and wasn't.)

[euzuro]

you're right, chris. the only place min/max zoom levels should be used is in the FixedZoomLevels descendent layers. Let's remove this.

[euzuro]

new patch added. up for review

[crschmidt]

I'd like to not remove this functionality, since we're already using it widely (including, I think, in examples). Instead, deprecate this, and in the deprecation warning, include a link to wikipage which documents the right way to do it.

Erik says he'll remake the patch.

[euzuro]

instead of removing, deprecate and warn. 3.0 here we come!!!!!

[euzuro]

tests pass in FF and ie6

[crschmidt]

Checked the warning, it wraps properly in firebug (yay) so this is good to commit.

[euzuro]

(In [4056]) deprecate use of 'minZoomLevels' in WFS layer. (Closes #672)