move texture load policy into RageTextureID, so it can be set to volatile consistently

for banners/backgrounds

stepmania/src/Sprite.cpp

@@ -54,6 +54,11 @@ RageTextureID Sprite::SongBGTexture( RageTextureID ID )
 	/* Song backgrounds are, by definition, in the background, so there's no need to keep alpha. */
 	ID.iAlphaBits = 0;
 
+	/* By default, song graphics are volatile: they're removed after one use.  This
+	 * is because some screens iteratively load and display lots of them (eg. ScreenSelectMusic,,
+	 * ScreenEditMenu) one at a time, and we don't want to have hundreds of banners loaded at once. */
+	ID.Policy = RageTextureID::TEX_VOLATILE;
+
 	// Don't we want to dither 16 bit textures at least?
 //	ID.bDither = true;
 
@@ -65,6 +70,8 @@ RageTextureID Sprite::SongBannerTexture( RageTextureID ID )
 	/* Song banners often have HOT PINK color keys. */
 	ID.bHotPinkColorKey = true;
 	ID.bDither = true;
+	ID.Policy = RageTextureID::TEX_VOLATILE;
+
 	return ID;
 }