Prepares P2P1SurrogateTaylorhoodStokesOperator for 3D
In the P2P1BlendingTaylorhoodStokesOperator we replace - P2ToP1ConstantDivzOperator div_z; - P1ToP2ConstantDivTzOperator divT_z; by - P2ToP1BlendingDivzOperator div_z; - P1ToP2BlendingDivTzOperator divT_z; For this the blending versions get typedefed in P1ToP2SurrogateOperator resp. P2ToP1SurrogateOperator. Note that while the forms are already implemented, the P2P1 operator will not work, as the variable operators themselves are currently only available in 2D in the master. However, IMHO this way is cleaner, as we have no hidden "wrong" imple- mentation, but get a nice and clean run-time abort.