GetSubstructMatches with dative bonds

[jhjensen2]

The following finds no matches:

m = Chem.MolFromSmiles('C1P->[Zr+3]<-1')
m.GetSubstructMatches(Chem.MolFromSmarts('C1P->[Zr+3]<-1’))

But all these work:

m.GetSubstructMatches(Chem.MolFromSmiles('C1P->[Zr+3]<-1’))

m.GetSubstructMatches(Chem.MolFromSmarts('[*]->[Zr+3]’))

m = Chem.MolFromSmiles('C1P-[Zr+3]-1')
m.GetSubstructMatches(Chem.MolFromSmarts('C1P-[Zr+3]-1’))

[greglandrum]

This is related to the way ring closures are handled in SMARTS parsing. That should be changed to make it consistent with the way the SMILES parser does things