Fix comment.
Make load_alignment( ) explicitly call load_from_file( ) first.
Remove unused function load_alignments(filenames,alphabets).
Add new function load_alignment(filename) that guesses the alphabet.
Fix alignment(a,sequences).
Use new alphabet guesser.
Refuse to guess alphabet if ATGCN fraction is between 0 and 95.
OK, allow all ambiguity codes.