has_multiplicative_inverse got lost

[iAmMichaelConnor]

In v0.3.6 or v0.3.7, the property has_multiplicative_inverse was removed from some concrete bignum parameter definitions in fields/ and in the rsa library. The default value of all 'preset' bignums is therefore has_multiplicative_inverse = true.
This might have been resolved with the refactor, but we should double-check.

(P.s. This is not the reason for the buggy rsa test; that's a different to-be-found bug).