various tweaks & fixes

Mostly for
https://github.com/libgdx/libgdx/issues/2359
https://github.com/libgdx/libgdx/issues/2524
https://github.com/libgdx/libgdx/issues/2441
https://github.com/libgdx/libgdx/issues/2436

`setUsePrototypes` already does this.