fasta2tcs: don't write the output file if there is an error
fasta2tcs: replace spaces in names by _
fasta2tcs: TCS now accepts ambiguity codes, fix validation
fasta2tcs: even though TCS claims to understand ambiguity codes, it replaces them by '?'

Do so in the conversion process to avoid the annoying warnings
fasta2tcs: display destination file even if provided on the command line