RSA: make XML keys use unsigned integers

PKCS1 / PKCS8 keys need *signed* integers because of section 8.3.3
at http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf#page=7
RSA: add unit test
RSA: update unit test
RSA: make unit tests perform string comparisons sans white space chars
RSA: syntax error in unit tests
Merge pull request #469 from terrafrost/rsa-xml-unsigned

RSA: make XML keys use unsigned integers

* terrafrost/rsa-xml-unsigned:
  RSA: syntax error in unit tests
  RSA: make unit tests perform string comparisons sans white space chars
  RSA: update unit test
  RSA: add unit test
  RSA: make XML keys use unsigned integers