Update copyrights in NOTICE.txt files to 2013.

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1458539 13f79535-47bb-0310-9956-ffa450edef68
Change 4.3-ALPHA1 -> 4.3-BETA1.

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1458541 13f79535-47bb-0310-9956-ffa450edef68