Cosmetic changes to FastaConverter and FastaConverterSuite.

Just making a few little cosmetic changes to FastaConverter, to make part of the code more readable.

Also, added a second condition to one of the tests in FastaConverterSuite, to check that the reassembled
sequence (which had been created, but wasn't being used) matched what was in the original file.

These changes are minor enough that I don't believe they need a separate entry in the CHANGES file.