proposal for replacing factory by a recent version from Singular github snapshot

-requires recent factory snapshot ( tarball sent to Dan)

update reason: bugfixes.

remaining issues:

 - find out how to avoid HAVE_CONFIG_H defines (currently required for building factory)
 - repair and enable broken showvar,showcf
 - pass correct FLINT location to libfactory in all cases (not only in case Flint is build by M2)

comments/suggestions?