Added support for RSA-SHA256, RSA-SHA384 and RSA-SHA512 signature algorithms. New hosted IdP metadata option 'signature.algorithm' to configure this, defaults to SHA1 for backwards compatibility.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3164 44740490-163a-0410-bde0-09ae8108e29a