Fixes issue #120.
The invertElementwise() method of the P1Function and P2Function class now allows the caller to select, whether the inversion should only be performed on DoFs interior to a primitive or also on a primitive's halo.
The invertElementwise() method of the P1Function and P2Function class now allows the caller to select, whether the inversion should only be performed on DoFs interior to a primitive or also on a primitive's halo.