SignatureReference inclusive_ns_prefixes not being copied

[mtheisen-solea]

According to the documentation:
To specify this value separately for reference canonicalizaition, pass a list of one or more [SignatureReference](https://xml-security.github.io/signxml/#signxml.SignatureReference) objects as the reference_uri keyword argument, and set the inclusive_ns_prefixes attribute on those objects.

This does not seem to be working.

Changing the following line seems to fix this.

signxml/signxml/signer.py

Line 322 in 5e0cc15

new_references.append(SignatureReference(URI=uri, c14n_method=reference.c14n_method))

needs to be changed to
new_references.append(SignatureReference(URI=uri, c14n_method=reference.c14n_method, inclusive_ns_prefixes=reference.inclusive_ns_prefixes))

[kislyuk]

Thank you for finding and reporting this issue, I really appreciate it. Fixed in v3.2.1, please test.