tests.

Also, Add the possibility to have several lustre files in the
command-line arguments.

remove the power operator.

Define a lustre.lus that contains a packaged version of Lustre
predefined operators. It will be in the standard lustre library,
and should be accessible directly (path).

For non-regression tests, do not use Lazycompiler.test function
anymore and just use  LazyCompiler.node_check instead.

put in the new file compiledDataDump.ml all the stuff
related to string convertions of CompiledData items.

src/lxm.ml:
src/global: (new file)
   Add the lustre file name in error messages.

src/compiledData.ml:
   Better Data structure dumping (string_of_type_eff,string_of_const_eff),
   and more dumping (LazyCompiler.check_const_interface).

src/lazyCompiler.ml:
   Fix a bug that prevented enum constants to be exported.
   Indeed, in LazyCompiler.const_check_interface_do, only extern
   constants (Extern_const_eff) were accepted in the provided part, whereas
   enum contants (Enum_const_eff) should also be accepted.

   Force constants interface checking in LazyCompiler.test.

src/test/Makefile:
src/test/onlyroll.lus:
src/test/heater_control.lus:
src/test/pfs.lus:
   Some more test files.