Changed Feature::overlaps so that all it does is a simple integer range comparison, ignoring the possibility that the features could be on different seq_regions.

this could have caused sequence caching problems

some changes for new schema and api

use arg strand in Slice::subseq so that SequenceAdaptor does reverse complimenting (it has more complete transliteration) rather than exon code

changed add_sub_SeqFeature method so that it no longer expects passed in feature to implement contains() method
This should allow Features to be used instead of SeqFeatures