Prepare ougoing xml's buffer before adding it to queue to reduce stream mutex contention.

git-svn-id: http://yate.null.ro/svn/yate/trunk@5805 acf43c95-373e-0410-b603-e72c3f656dc1
Merge branch 'upstream' of github.com:vir/yate into deb
Updated debian package version to 5.2.1~svn5805