Adds make and rebuild Ant targets to the build.xml of libjitsi which implement incremental and clean compiling and packaging of the libjitsi library.

On behalf of Vincent Lucas, commits a fix to the calculation of the Last SR (LSR) timestamp for the Sender Report RTCP packet.

Commits an initial version of the libjitsi library which should be fully functional with respect to neomedia/MediaService and should be usable with and without OSGi.