Location/Split: Added its own "length" subroutine to
handle more complicated cases like cut by origin locations,
which were returning the whole sequence length
(e.g. "join(161..200,1..5))" returned 200 instead of 45).
For transpliced locations (e.g. "join(16..20,complement(6..10))"),
since exons can even be in different chromosomes, it returns
the sum of the lengths of the individual segments. Added tests.