Java's desktop integration on Linux relies on dlopen'ing some libraries (gtk2 or
gnome). This commit makes Java able to find gtk2, fixing the problem of Jitsi's
system tray icon not appearing.
Part of bug #4014.
Close#9754.
Otherwise, the wrong directory is changed into, and trying to start Jitsi gives:
$ jitsi
Error: Could not find or load main class net.java.sip.communicator.launcher.SIPCommunicator