Fixed two bugs with signing Shib 1.3 responses. 1) certificate chain bug 2)...

Fixed two bugs with signing Shib 1.3 responses. 1) certificate chain bug 2) switched to sign responses instead of assertions

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@235 44740490-163a-0410-bde0-09ae8108e29a