* New playlist import/export system:
   -export plugin in misc/playlist (contains one module for each file type)
   -open plugin = special demuxer2, that can be opened from the command
    line or the graphical interface.
  NB: the demuxer "playlist" is forced to earn speed, but this does not
  work yet, as we have a demux2

* modules/gui/wxwindows: use the new import/export.

* src/playlist/group.c : fixed boundary check

* src/playlist/item-ext.c: correctly reset stuff when clearing the playlist