Update copyrights in NOTICE.txt files to 2013

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/branches/4.2.x@1458727 13f79535-47bb-0310-9956-ffa450edef68
Change 4.2.3 -> 4.2.4

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/branches/4.2.x@1458728 13f79535-47bb-0310-9956-ffa450edef68