* Added gprof profiling support with --enable-profiling.

    It works at last! configure with --enable-profiling, build, run
 vlc (you may want to add --noaudio, it currently segfaults with sound
 here) and launch "gprof vlc" when finished.

    To make gprof work with multithreaded programs, one needs to set the
 internal ITIMER_PROF timer for each new thread launched. I did this
 through a wrapper in vlc_thread_create (see include/threads.h).