configure script changes

[Dr . Jürgen Sauermann]

    Hi,
      
      as some of you may have noticed already, there were some changes
      in
      the ./configure script of GNU APL:
      
      1. more comments inside the script (file: configure.ac)
      2. more structured output and increased verbosity, and
      3. move of some script variables into their own namespace apl_
      (as suggested
        in the autoconf manual). This will continue for a while, since
      many variables
        still live outside the apl_ namespace.
      
      The ./configure cases were either all or none of the optional
      libraries
      are present seem to be working. The mixed cases, where some
      optional
      libraries are present and others, could still contain some quirks,
      though.
      
      Please keep reporting them as they occur.
      
      Best Regards,
      Jürgen