First run of GF "FlintBig"

This commit requires --enable-flint (which will be the default soon).
RingElement's in the engine did not have their hash values computed.

This is now done, however, it is not complete yet: need to have less
hash collisions (e.g. between monomials), and also other types need to
have this bug fixed too.
GF Flint Big, more functions done.

More to come too.