* ./configure.ac.in: removed now unnecessary --force-exe-suffix flag.

  * ./src/misc/objects.c: structure_lock is now local.
  * ./src/misc/threads.c: implemented named mutexes which provide a handy
    way to protect data across plugins which might be sharing the same
    resources. Thread-unsafe libraries come to mind, but we can imagine
    using a named mutex for configuration files, or special devices.
  * ./include/main.h: removed global_lock because of vlc_mutex_need, removed
    p_global_data because it was never used, removed structure_lock because
    it did not belong here.