minor updates Makefile, gnuplot/circle, pca_input.dat, quoting.c
 pca-v2.1.1  Important data structure change in PCA and LIBAL

    eliminated complex header text structures t_tag, t_headers, ...
    replaced them with simple char ** headers type variables
    they are pointers to arrays of strings
    This will imply changes in LIBAL (t-headers & t_tag no longer
    needed, not done yet) and more importantly bug corrections
    in LIBSTTRING.
    LIBSTRING.C was corrected:  get_token() now allocates new memory
    for the words, instead of using the input string memory space
    which didn't work when input string was non static.