URLBuilderify textpane, crazy

Change-Id: I97b1f1866cfb9250885582815bc47596abbfb98c
Reviewed-on: http://gerrit.dmdirc.com/412
Tested-by: Gregory Holmes <greboid@dmdirc.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>
Tested-by: Chris Smith <chris@dmdirc.com>

src/com/dmdirc/addons/ui_swing/textpane/TextPaneCanvas.java

 import com.dmdirc.config.ConfigManager;
 import com.dmdirc.interfaces.ConfigChangeListener;
 import com.dmdirc.ui.messages.IRCTextAttribute;
+import com.dmdirc.util.URLBuilder;
 
 import java.awt.Cursor;
 import java.awt.Graphics;
             @Override
             public void run() {
                 backgroundImage = backgroundPath.isEmpty() ? null : Toolkit.
-                getDefaultToolkit().getImage(backgroundPath);
+                getDefaultToolkit().getImage(URLBuilder.buildURL(backgroundPath));
                 repaint();
             }
         });