WhitneyAVSolver: The nonlinear iteration can now use the stopping criterion ||b-A(V)V|| / ||b|| with V the current nonlinear iterate. Only parallel implementation is ready.

git-svn-id: svn://svn.code.sf.net/p/elmerfem/code/trunk@6701 04224531-1f84-46d8-96ce-875b9e37dce3