More consistent error messages, with failure explanation

and a little bit of housekeeping (tabs, etc)
Small fix for previous commit
GuessSeqFormat from non-seekable filehandles such as STDIN
Update and modernization of GuessSeqFormat tests
Small test fix
Checked that all testable formats are tested
Removed test data files that are not needed anymore
Restored test file for AlignIO
Fixed a typo
Reorganized guess() method of GuessSeqFormat
Updated number of tests