Preliminary implementation of issue #38 (unknown exon offsets).

This is a rebase of commit r202 to the current branch. Please not that this
is not a very clean implementation and still contains several Todo's. But
they don't affect functionality outside issue #38.

Please see the issue for more information.



git-svn-id: https://humgenprojects.lumc.nl/svn/mutalyzer/branches/refactor-mutalyzer-branch@325 eb6bd6ab-9ccd-42b9-aceb-e2899b4a52f1