Changes `ppm2fli_b1.92' --> `ppm2fli_2.0d':

1.) On some DEC systems the popen call failed due to a "b" in the mode
    specifier of a `popen' statement. Because of that the reading through a 
    filter could not be used. With the current version the filter options
    should also work on DEC systems.

2.) When reading raw PBM data (black/white) and the image width was not
    a multiple of eight, the pictures became currupted in the old version.
    The input of raw PBM is modified now, so that PBM images with an odd
    width should work too.

3.) The output section of the `unflick' program was changed, so that now
    different external filters can be used for writing the file. The old 
    version allowed only `gzip' and `compress'.

Changes `ppm2fli_2.0d' ---> `ppm2fli-2.1'

No functional changes. Now distribution of the software under the terms of 
the GNU General Public License.