Update Issue 21
(git-repo)
http://java.net/jira/browse/JSIP-443

Committing patch from mitchell.ackerman@pgi.com, Thanks !
 and adding non regression test

git-svn-id: https://svn.java.net/svn/jsip~svn/trunk@2269 8e71dc83-d81e-6649-80f2-80b843a9b2be
Bug 622: No media due to JSIP sending repeated ACK

The ACKs were dropped because CSeq numbers got out of order.  Fix is to prevent this from happening by preventing CSeq numbers from ever decreasing