New feature: parsing of MTRIXn/_struct_ncs_oper records, 
generally used for viral proteins in order to generate the full AU
Improved the unique xtal interfaces calculation
Reduced memory usage of unique interfaces calculation
Merge branch 'master' of https://github.com/biojava/biojava
- add isValidSequence method into CompoundSet interface. Implemented.
- add deprecated annotation on  verifySequence