Acd/atomlabels

Stuff to read the non-standard ACD/Labs atom label property (M  ZZC) in molfiles generated by ACD/ChemSketch. I've tested it fairly extensively, but as MDLV2000Reader is a strategically-important class in the CDK, any further testing would be greatly appreciated.
The new code throws a CDKException if the ZZC property is found while reading in STRICT mode. If preferred, I could change this to just print a warning and skip the labels, just let me know. There were plenty of precendents in the code to go the exception route.