Memory

 - Sync extern/shiny. Aside from some misc improvements, this adds a method to periodically unload materials that are not referenced, potentially allowing the textures used by those materials to get unloaded.
 - Set memory budget values for Texture and Mesh managers (part of http://bugs.openmw.org/issues/279). For this to actually have an effect, we need changes that have just been pulled into Ogre 1.9.