Added an additional check in the transform method. When testing exons, if...

Added an additional check in the transform method. When testing exons, if consecutive exons in the old version of the transcript were on the same strand then the new versions should be on the same strand too. If not, returns undef. Prevents cases being transformed where the transcript's exons map as below:

1
------------------------------
-1        5  4  3  2  1

to

1      3  4  5
------------------------------
-1               2  1