Log Message:
Updated ocaml-lablgtk to 2.18.4.

Remove camlp4 dependency (see changelog below).

In Lablgtk-2.18.4:

2016.04.27 [Jacques]
  * disable camlp4 make rule when no camlp4o available
  * update applications
  * rename GC module to GMain.Gc_custom

2016.04.11 [Jacques]
  * Fix ml_gnome_canvas_c2w (Didier Le Botlan)

2016.03.06 [Jacques]
  * remove build dependency on camlp4 (still needed for tree version)
  * allow to change the GC speed (i.e. the impact of custom blocks)
    see GMain.GC.set_speed.

2016.03.04 [Jacques]
  * use own definition of alloc_custom, to be sure to allocate in the heap

2015.04.16 [Jacques]
  * fix GtkTree.TreeModel.cast

2015.02.06 [Jacques]
  * add get_image and get_pixbuf to GDraw.drawable.

In Lablgtk-2.18.3:

2014.10.06 [Jacques]
  * add Gdk.Window.create_foreign and set_transient_for functions
    (Tim Cuthbertson)

2014.09.20 [Jacques]
  * CAMLparam initializes with Val_unit rather than 0 since ocaml 4.02.
    Fix a related problem in ml_gobject.
    This caused random crashes with unison (Christopher Zimmermann, PR#1425)

  * Also factorize some code to use Val_option_*
  * Replace XID by GdkNativeWindow where required.
    You may need to insert calls to Gdk.Window.native_of_xid in some places.

In Lablgtk-2.18.2:

2014.09.17 [Jacques]
  * Revert old commit which broke notify signals
  * Quote $(FLINSTALLDIR) in Makefile (cf PR#1342)
  * Update applications/browser for 4.02

2014.08.22 [Jacques]
  * Make Float_val an alias for Double_val, since it was used
    wrongly anyway (Felix Ruess)
  * Make GObj.misc_ops#add_accelerator polymorphic in the widget of
    the signal (Erkki Seppala)
  * Use properties in GtkAdjustment, rather than direct accessors

2013.12.31 [Jacques]
  * fix GtkTree.IconView.get_path_at_pos (Thomas Leonard)