lnodes_is_valid: Now handling of return value of MPI-function.
lnodes_is_valid: sc_array lookups now use the sc_array_index functions
lnodes_is_valid: now checking face_code bits.
lnodes_is_valid: does not use pow for integers anymore.
lnodes_is_valid: Added comments.
Minor changes to p4est_lnodes_is_valid
Add todo on lnodes_is_valid