Indexing monomial coefficients must check for garbage

[mattsignorelli]

GTPSA plays a lot of clever tricks to speed things up, and certain monomials may contain garbage when not "in use" . So checking if the monomial is garbage must be performed (and returned as 0 if it is garbage)
This can be done using mad_bit_tst given the order of the monomial and nz in the tpsa:

if (!mad_bit_tst(a->nz,o)) return 0.0

[mattsignorelli]

Unfortunately this function is inlined and not exported

[mattsignorelli]

Issue submitted upstream, getter functions mad_tpsa_getv getm, etc should check for nz