more robust, pre-existing niftio routine

Changed the way that ascii matrices are read, so that it is now a little stricter in enforcing the numerical rows to each have the same number of entries, but allowing non-numerical rows (comments) in the middle

Changed get_sortindex function to use a strictly less than function based _only_ on the first element of the pair

Put in a fix in skip_alpha to allow it to cope with eof conditions and hence read one line files correctly