Apron wrapper for PPLite 0.12.

[ezaffanella]

PPLite version 0.12 no longer depends on gmpxx (the C++ interface of GMP).

Note: we also applied a minor renaming to newpolka matrix_* type and functions (adding prefix "pk_") so as to avoid a few name clashes with version 3 of the FLINT library, which is a required dependency of PPLite. Both newpolka and FLINT v.3 have functions named "matrix_clear" and "matrix_equal", thereby preventing static linking of Apron and PPLite when using the newer version of FLINT. Fix contributed by Michele Spotti.