Merge pull request #24 from ichthyos/master

Throw IE- and Safari-friendly error upon finding invalid dimensions.

jquery.flot.js

@@ -716,7 +716,7 @@
             canvasHeight = placeholder.height();
             
             if (canvasWidth <= 0 || canvasHeight <= 0)
-                throw "Invalid dimensions for plot, width = " + canvasWidth + ", height = " + canvasHeight;
+                throw new Error("Invalid dimensions for plot, width = " + canvasWidth + ", height = " + canvasHeight);
         }
 
         function resizeCanvas(c) {