Fix slider glitch on clever skins

Some skins took advantage of the fact that they could make the bmp files
smaller to make certain elements transparent. This fixes allows that trick to
work for the volume and balance sliders.

Fixes #64

winamp.css

@@ -303,6 +303,7 @@ a:focus { outline: none; }
     /* background-image: VOLUME.BMP via Javascript */
     background-position: -15px -422px;
     cursor:url('cursors/VOLBAR.CUR'), auto;
+    background-repeat: no-repeat;
 }
 #volume::-moz-range-thumb {
     margin-top: 1px;
@@ -311,6 +312,7 @@ a:focus { outline: none; }
     /* background-image: VOLUME.BMP via Javascript */
     background-position: -15px -422px;
     cursor:url('cursors/VOLBAR.CUR'), auto;
+    background-repeat: no-repeat;
 }
 #volume:active::-webkit-slider-thumb  {
     background-position: 0 -422px;
@@ -336,6 +338,7 @@ a:focus { outline: none; }
     /* background-image: VOLUME.BMP via Javascript */
     background-position: -15px -422px;
     cursor:url('cursors/POSBAR.CUR'), auto;
+    background-repeat: no-repeat;
 }
 #balance::-moz-range-thumb {
     top: 1px;
@@ -344,6 +347,7 @@ a:focus { outline: none; }
     /* background-image: VOLUME.BMP via Javascript */
     background-position: -15px -422px;
     cursor:url('cursors/POSBAR.CUR'), auto;
+    background-position: no-repeat;
 }
 
 #balance:active::-webkit-slider-thumb  {