Added Message.handlers() function to return list of installed message handlers.


git-svn-id: http://yate.null.ro/svn/yate/trunk@5878 acf43c95-373e-0410-b603-e72c3f656dc1
Merge branch 'upstream' of github.com:vir/yate into deb
Updated debian package version to 5.3.1~svn5878