fix for #650 - if user specifies a layer as transparent and of format image/jpg, we change it to the appropriate type (gif or png). Sure, it's somewhat magical... but it will probably help people out in the long run

git-svn-id: http://svn.openlayers.org/trunk/openlayers@3554 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/WMS/Untiled.js

@@ -74,13 +74,23 @@ OpenLayers.Layer.WMS.Untiled.prototype =
                        OpenLayers.Util.upperCaseObject(this.DEFAULT_PARAMS)
                        );
 
-        // unless explicitly set in options, if the layer is transparent, 
-        // it will be an overlay        
-        if ((options == null) || (options.isBaseLayer == null)) {
-            this.isBaseLayer = ((this.params.TRANSPARENT != "TRUE") && 
-                                (this.params.TRANSPARENT != "true") && 
-                                (this.params.TRANSPARENT != true));
+        //layer is transparent        
+        if (this.params.TRANSPARENT && 
+            this.params.TRANSPARENT.toString().toLowerCase() == "true") {
+            
+            // unless explicitly set in options, make layer an overlay
+            if ( (options == null) || (!options.isBaseLayer) ) {
+                this.isBaseLayer = false;
+            } 
+            
+            // jpegs can never be transparent, so intelligently switch the 
+            //  format, depending on teh browser's capabilities
+            if (this.params.FORMAT == "image/jpeg") {
+                this.params.FORMAT = OpenLayers.Util.alphaHack() ? "image/gif"
+                                                                 : "image/png";
+            }
         }
+
     },    
 
     /**