Do not activate mkv-preload-local-dir by default.

 It will avoid VLC loading every .mkv in the same directory than the
one you are trying to play (can be very very long).
Of course, this will break linked mkv files...

modules/demux/mkv/mkv.cpp

@@ -55,7 +55,7 @@ vlc_module_begin ()
             N_("Chapter codecs"),
             N_("Use chapter codecs found in the segment."), true );
 
-    add_bool( "mkv-preload-local-dir", 1, NULL,
+    add_bool( "mkv-preload-local-dir", 0, NULL,
             N_("Preload Directory"),
             N_("Preload matroska files from the same family in the same directory (not good for broken files)."), true );