clean up RageDisplay methods, add ability to mask song banner

The masking uses the Z-buffer under the assumption that some cards don't have a stencil.  Should we be using the stencil instead?  It doesn't really matter because we never need both the Z buffer and stencil buffer simultaneously.

stepmania/src/BitmapText.cpp

@@ -280,14 +280,9 @@ void BitmapText::DrawPrimitives()
 		return;
 
 	DISPLAY->SetTextureModeModulate();
-	if( m_bBlendAdd )
-		DISPLAY->SetBlendModeAdd();
-	else
-		DISPLAY->SetBlendModeNormal();
 
-	/* Draw if we're not fully transparent or the zbuffer is enabled (which ignores
-	 * alpha). */
-	if( m_temp.diffuse[0].a != 0 || DISPLAY->ZBufferEnabled())
+	/* Draw if we're not fully transparent or the zbuffer is enabled */
+	if( m_temp.diffuse[0].a != 0 )
 	{
 		//////////////////////
 		// render the shadow