* doc/ref_guide/ref_guide.mk (ref_guide_dependencies):
	New variable.
	Use it to define dependencies of...
	($(REF_GUIDE_HH), $(REF_GUIDE_PDF)):
	...these targets.
	* doc/technical/technical.mk (technical_dependencies):
	New variable.
	Use it to define dependencies of...
	($(TECHNICAL_HH), $(TECHNICAL_PDF)):
	...these targets.
	* doc/tutorial/tutorial.mk (tutorial_dependencies):
	New variable.
	Use it to define dependencies of...
	($(TUTORIAL_HH), $(TUTORIAL_PDF)):
	...these targets.