Removed unnecessary canvas skipPositioning flag.

The primary canvas uses position: absolute while the overlay canvas does
not.  This can cause the two to get out of alignment in rare cases when
floating elements are placed near the plot placeholder.  There doesn't
appear to be any reason why the overlay can't also be
absolutely-positioned, so I've just removed the flag entirely.

jquery.flot.js

@@ -738,15 +738,13 @@ Licensed under the MIT license.
             return devicePixelRatio / backingStoreRatio;
         }
 
-        function makeCanvas(skipPositioning, cls) {
+        function makeCanvas(cls) {
 
             var c = document.createElement('canvas');
             c.className = cls;
 
-            if (!skipPositioning)
-                $(c).css({ position: 'absolute', left: 0, top: 0 });
-
-            $(c).appendTo(placeholder);
+            $(c).css({ position: 'absolute', left: 0, top: 0 })
+            	.appendTo(placeholder);
 
 			// If HTML5 Canvas isn't available, fall back to Excanvas
 
@@ -842,8 +840,8 @@ Licensed under the MIT license.
 
                 getCanvasDimensions();
 
-                canvas = makeCanvas(true, "flot-base");
-                overlay = makeCanvas(false, "flot-overlay"); // overlay canvas for interactive features
+                canvas = makeCanvas("flot-base");
+                overlay = makeCanvas("flot-overlay"); // overlay canvas for interactive features
 
                 reused = false;
             }