E.g., when creating a fresh var using the name of "L1", I was creating a var names "_L11", and then
"_L12", and so on. But if a var is named "L11", "_L111" is created. If if "L1" is used to generate
11 frash vart names, the name "_L111" clashes !!!

The fix contist in adding an underscore before : "L1" produces "_L1_1", "_L1_2", ..., and "_L1_11".

nb : the naming scheme is still wrong for other reasons... Next fix.

Add Some lustre files that are automatically tested thanks to the
generic Makefile (from the Youssef compiler).

Test files are organized as follows :

 - files in directories that are under the "should_fail" directory
  do triggers errors, but it is intented

	should_fail/syntax
	should_fail/type
	should_fail/semantics

 - and files that should not trigger any error:

	should_work/