Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56982
Merged revision(s) 1624984 from tomcat/trunk:
Return the actual negotiated extensions rather than an empty list for Session.getNegotiatedExtensions()

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1625878 13f79535-47bb-0310-9956-ffa450edef68