bug fix: still adjust coords for exon that is wholly consumed by introduced frameshift intron b/c coords are used later for transcript splitting.

added a sub_Slice method, that returns a smaller slice. This will not make use of the cached features of the parent slice though

just gene, transcript, and exon table;

to enable lazy loading

removed warning for shared exons

Made check for insertion failure stricter. sth->execute could return "0E0" which perl evaluates as true but zero (fix from lec)

fix: briggsae contig<->clone assembly table info was incorrect because embl_offset was not set in source database