fixed masking bug in Seq2SeqEdge.items(); made identity computation case-insensitive; added conservedSegment() method.
fixed masking bug in Seq2SeqEdge.items(); made identity computation case-insensitive;
added conservedSegment() method.

ctb/pygr,ctb/pygr,theoryno3/pygr,ctb/pygr,GenDataPro/pygr,RitwikGupta/pygr,theoryno3/pygr,RitwikGupta/pygr,GenDataPro/pygr,ctb/pygr,cjlee112/pygr,ctb/pygr,cjlee112/pygr,GenDataPro/pygr,RitwikGupta/pygr,theoryno3/pygr,cjlee112/pygr,cjlee112/pygr