It now is disabled if:
-Lacking hardware support for FBOs
-RenderDeferred not permitted in gpu feature table
-RenderAvatarVP not permitted in gpu feature table
-VertexShaderEnable is enabled and permitted in gpu feature table
-WindLightUseAtmosShaders is enabled and permitted in gpu feature table
Enabling deferred now requires WindLightUseAtmosShaders to be on beforehand, instead of blindly enabling it.