Check excitation is symmetry allowed when calculating matrix elements.
Check excitation is symmetry allowed when calculating matrix elements.

Otherwise (as the warning in the function interface says!) we can get
garbage instead of 0 when looking up something zero by symmetry.

hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande