Those two versions have a bug in memory allocation. The bug appears when
changing the allocation functions back and forth. In the beginning, MPFR
3.1.4 and 3.1.5 gather the GMP allocation functions and always use them. If
they are changed, MPFR does never notice that. This behavior was removed in
a patch to 3.1.5, what means that everything should be OK with MPFR 3.2.0.
The obsolete and unused code was removed. The interface was cleaned. The
memory leaks dissapeared (according to valgrind), because the pointers
to RS memory were removed.
For test purposes, the rational interface is not tested.