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
SSH2: rm unused constant

it doesn't need to be defined since the strlen($this->last_interactive_response)
check in _login_helper serves the same purpose that NET_SSH_MASK_LOGIN_INTERACTIVE
was intended to serve
Merge pull request #470 from terrafrost/ssh2-rm-unused-constant

SSH2: rm unused constant

* terrafrost/ssh2-rm-unused-constant:
  SSH2: rm unused constant
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
README: update download link to 0.3.8
ASN1: fix issue with non-constructed context-specific tags
ASN1: add unit test for non-constructed context-specific change
ASN1: fix unit test
Merge pull request #480 from terrafrost/asn1-fix

ASN1: fix issue with non-constructed context-specific tags

* terrafrost/asn1-fix:
  ASN1: fix unit test
  ASN1: add unit test for non-constructed context-specific change
  ASN1: fix issue with non-constructed context-specific tags
BigInteger: accomodate GMP change in PHP 5.6
Merge pull request #482 from terrafrost/gmp-56

BigInteger: accommodate GMP change in PHP 5.6

* terrafrost/gmp-56:
  BigInteger: accomodate GMP change in PHP 5.6
SSH2: removed redundant rtrim
Merge pull request #483 from cezarykluczynski/ssh2-rtrim-strip

SSH2: removed redundant rtrim

* cezarykluczynski/ssh2-rtrim-strip:
  SSH2: removed redundant rtrim
Fix Net_SFTP::filetype() block device recognition.
Merge pull request #486 from vvolodko/patch-1

Fix Net_SFTP::filetype() block device recognition.

* vvolodko/patch-1:
  Fix Net_SFTP::filetype() block device recognition.
Correct constant: NET_SFTP_BLOCK_DEVICE -> NET_SFTP_TYPE_BLOCK_DEVICE