libnotify plugin need to initialize dbus threads system
libnotify uses dbus, and if 2 or more threads are using the same D-Bus connection, D-Bus library needs to be initialized to use threads with dbus_threads_init()
when 2 notify events are sent in a short amount of time without initializing libdbus threads system first, this makes vlc crash in libdbus.
dbus 1.0.0 provides dbus_threads_init_default() to do that easily, but 0.9.2 doesn't have and need to be passed a set of functions to handle mutexes and condition variables: mutex_new mutex_free mutex_lock mutex_unlock condvar_new condvar_free condvar_wait condvar_wait_timeout condvar_wake_one condvar_wake_all
some code can be taken from the dbus bindings, like glib and qt.
Other possibilities are: enable only libnotify if D-Bus has dbus_threads_init_default() or implement a queue of events in notify.c to make use of libnotify in only one thread.