Ensure api returns api object and not subclasses of it.

git-svn-id: http://csipsimple.googlecode.com/svn/trunk/CSipSimple@2323 9f815046-5998-e9c0-b7e2-ac03a23edfa4
Fixes issue 2522. Add local nat type.

git-svn-id: http://csipsimple.googlecode.com/svn/trunk/CSipSimple@2324 9f815046-5998-e9c0-b7e2-ac03a23edfa4