Assume stranded features for bad LOCUS link GenBank files.

i.e. Default to assuming nucleotides (and so stranded features)
rather then amino acids (where the protein features have no strand)

Based on an issue reported by Kai Blin.

Unit test to follow...
Adding test case from Kai Blin; Fixed some warnings.

This test GenBank file with an invalid LOCUS line lets
us test the strand behaviour fixed in the previous
commit.

Some generic warnings from the GenBank parser should
have been BiopythonParserWarning - and thus silenced
in the unit tests.

Also fixed line lengths for some other GenBank warnings.