Upgrading XStream to 1.4.6

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_1_X@1552989 13f79535-47bb-0310-9956-ffa450edef68
Merge from 1_1_X

git-svn-id: https://svn.apache.org/repos/asf/syncope/trunk@1552992 13f79535-47bb-0310-9956-ffa450edef68