added a labelOutlineOpacity attribute to SVG and Canvas Renderers.

lib/OpenLayers/Renderer/Canvas.js

@@ -712,6 +712,7 @@ OpenLayers.Renderer.Canvas = OpenLayers.Class(OpenLayers.Renderer, {
             for (var i = 0; i < numRows; i++) {
                 if (style.labelOutlineWidth) {
                     this.canvas.save();
+                    this.canvas.globalAlpha = style.labelOutlineOpacity || style.fontOpacity || 1.0;
                     this.canvas.strokeStyle = style.labelOutlineColor;
                     this.canvas.lineWidth = style.labelOutlineWidth;
                     this.canvas.strokeText(labelRows[i], pt[0], pt[1] + (lineHeight*i) + 1);

lib/OpenLayers/Renderer/SVG.js

@@ -655,6 +655,9 @@ OpenLayers.Renderer.SVG = OpenLayers.Class(OpenLayers.Renderer.Elements, {
             outlineStyle.fontColor = outlineStyle.labelOutlineColor;
             outlineStyle.fontStrokeColor = outlineStyle.labelOutlineColor;
             outlineStyle.fontStrokeWidth = style.labelOutlineWidth;
+            if (style.labelOutlineOpacity) {
+                outlineStyle.fontOpacity = style.labelOutlineOpacity;
+            }
             delete outlineStyle.labelOutlineWidth;
             this.drawText(featureId, outlineStyle, location);
         }