Fix #143 Allow the combination of X509Data and KeyValue when they represent the same public key

[lscorcia]

Hi, this is a shot at implementing the suggested logic fix for issue #143. Basically the code now extracts the key parameters for both key representations and compares them to decide whether they are the same key or not.

If the match is positive, then the code goes on as if there were no ambiguity. If the match is negative, the ignore_ambiguous_key_info parameter lets the user decide whether to validate using the X509 data only.

Please bear in mind that this is my first python code ever, so I apologize in advance for any stupid mistake I may have made. I have tested it only using RSA signatures. Also some minor code duplication is introduced and it probably could use some refactoring, but I have to say I don't know python well enough to improve this code. Please review it carefully.

Thanks in advance for your work and your time!

[kislyuk]

Thank you for your work here @lscorcia. This looks like a very good start, and I appreciate your contribution. Before I can release this, it will require a test case and a refactoring to reduce duplication as you mentioned. I am merging this now since I would rather have this in the main branch and work on it there.

Please let me know if you can contribute a test case or test data with a positive (valid signature) and negative (mismatch) cases.