Augment r618 by allowing the more prosaic and self-documenting { maxResolution: 'auto' }.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@619 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -89,7 +89,7 @@ OpenLayers.Map.prototype = {
 
         this.updateSize();
         // make the entire maxExtent fix in zoom level 0 by default
-        if (this.maxResolution == null) {
+        if (this.maxResolution == null || this.resolution == "auto") {
             this.maxResolution = Math.max(
                 this.maxExtent.getWidth()  / this.size.w,
                 this.maxExtent.getHeight() / this.size.h );