MT#7347 added reference counting to plug-in interfaces.

Fixes crash on restart. Included upstream commits:

commit b9cda79c435fc002c259b5430e61c45d8e94aa2c
Author: Raphael Coeffic <rco@iptel.org>
Date:   Sun Apr 28 14:27:27 2013 +0200

    sip: add reference counting to transport sockets

    allows for dynamic socket creation/deletion.

commit 73490566761bb0fb09a6ebd74566d7f2b789c62f
Author: Raphael Coeffic <rco@iptel.org>
Date:   Tue Nov 20 15:33:35 2012 +0100

    c/f: correcting some strange scope issues encountered with GCC & clang on osx.

commit 0b2c8068a980058ff34655bc4928aeaedbe527d7
Author: Stefan Sayer <stefan.sayer@googlemail.com>
Date:   Thu Jan 5 22:10:52 2012 +0100

    b/f: don't delete registered app objects, e.g. DSM apps

    fixes bug #68
    https://bugtracker.iptel.org/view.php?id=68
MT#7347 bump version to 1.4.3+spce2.8.3 in 2.8 branch