Fixed error in the writing of ASCII table columns where all of the elements of the table were null or 0 length strings. Previously we would write a column with TFORM A0. This is not supported by CFITSIO and since it is not valid Fortran is of dubious legality for FITS. Such columns are now written with A1 (issue noted by Jason Weiss, UCLA). AsciiTable did not check if columns were of a valid type (if the FitsFactory methods were used, then a BinaryTable would be written, but a user can explicitly instantiate an AsciiTable). A FitsException is now returned if a column other than a String, double, int or long array is used.