Prepare sign and ecp verify sign for soap.

Added functionality to prepare signature for a authn request, without
signing. This makes it possible to sign the authn request within a SOAP
message instead. To verify a authn request in a ecp it have to validate
the whole SOAP message and not just the authn request. Added logic to
sen the original xml document to the validation function.
Merge pull request #27 from HaToHo/master

Prepare signature for authn request. Verify signature for ecp.
To make it work with Python 2.6
Spurious print statement removed
decrypt() expects a string not an xmlenc.EncrypedData
Merge pull request #28 from rectalogic/decrypt_string

decrypt() expects a string not an xmlenc.EncrypedData
Attempt at catching knowledge about SAML errors in the middleware.
PEP-8 compliance
Improve documentation
Added HTTP response class.
Editorial
Merge branch 'master' of github.com:rohe/pysaml2
Use a custom exception for unsolicited response so we can capture it and show a nicer screen to the user than just an 500 error message