build: Add a common script for generating OCaml dependencies correctly.

These are generated in many different ways in the various
subdirectories, and sometimes not generated correctly.  Introduce a
script to do this in one place, and hopefully correctly.

This is mostly simple refactoring, but I got rid of a couple of
things:

(1) The ‘make depend’ rule doesn't appear to be needed.  automake (or
make?)  seems to rebuild the ‘.depend’ file automatically just because
it is included.

(2) I got rid of the hairy path rewriting sed expression.  Possibly
that is needed for srcdir != builddir.

ocaml/Makefile.am

@@ -185,17 +185,8 @@ guestfs.cmx: guestfs.ml
 	$(guestfs_am_v_ocamlopt)$(OCAMLFIND) ocamlopt $(OCAMLOPTFLAGS) -package unix -c $< -o $@
 endif
 
-depend: .depend
-
-.depend: $(wildcard $(abs_srcdir)/*.mli) $(wildcard $(abs_srcdir)/*.ml) $(wildcard $(abs_srcdir)/t/*.ml)
-	rm -f $@ $@-t
-	$(OCAMLFIND) ocamldep -I ../ocaml -I $(abs_srcdir) $^ | \
-	  $(SED) 's/ *$$//' | \
-	  $(SED) -e :a -e '/ *\\$$/N; s/ *\\\n */ /; ta' | \
-	  $(SED) -e 's,$(abs_srcdir)/,$(builddir)/,g' | \
-	  sort > $@-t
-	mv $@-t $@
-
+.depend: *.mli *.ml
+	$(top_builddir)/ocaml-dep.sh $^
 -include .depend
 
 SUFFIXES = .cmo .cmi .cmx .ml .mli .mll .mly