Start refactoring sources and move all code that depends an external libraries and can be switched at runtime in the plugins/ directory.

(Clears the type and compile environment, the compilation unit table, the table of named types and reset to their default values).

Minor tweaks and add the file driver/cduceeditor_js_runtime.ml that was previously not added to the repository because of a buggy .gitignore entry.

One can pass the undocumented --allow-cduce-unsafe-ns to the compiler
to use these primitive directly.

Make use of the new recursive dependency building flags to avoid listing the order of .cdo in the Makefile (used for the standard library)

If A.cd relies on B.cdo and B.cd is found in the object path, then B.cd is compiled automatically.

Modify the Makefile to automatically rebuild OCaml objects when some Make Variable they depend on changes.

Implement hash-consing of big_ints. This allows us to know the set of all big_ints constants that are used
by a program and to serialize them as string (fix a compatibility issue with js_of_ocaml).
This could also lead to some optimizations when computing expensive big_ints.

Make the generated .cdo files compatible with 32 bits version of OCaml, and hopefully with js_of_ocaml.

Need to do the same for Numbers, Booleans, and then Objects.

Modified files to make a primitive from register_event.
register_event in progress (start 2)

	- in compile/operators.ml : register_fun3 (id register_fun2 with 3 args)
	- compute_depend (has been modified)
	- in runtime/cduce_js.ml :
		- load_from_dom
		- replace_inner
		- replace_outer
		- test_register3
		- define_prims (Js function)
	- in runtime/print_xml.ml and types/builtin.ml :
		Adding functions developped in previous file as primitives

	* Add load_from_dom correctly implemented (not yet functionnal)
	* Add replace_inner (innerHTML)
	* Add replace_outer (outerHTML)