"typedef exists but its value is not_found" and "typedef is
	not found because it does not exist".

- tests/case.cc: New file.
- tests/switch.cc (where_): Precise name.
- tests/ret.cc: New file.
- mlc/bool.hh (assert): Remove is_true to avoid cryptic error
message such as "is_true" inaccessible.
- mlc/flags.hh (found): New class.
- mlc/typedef.hh (result2): New inner class to disambiguate between
"typedef is found but its value is not_found" and "typedef is not
found".
(mlc_ret, mlc_decl_typedef(ret)): Move to...
- mlc/ret.hh: ...this new file.
- mlc/switch.hh: Change that makes this file soon obsolete.
- mlc/case.hh: New file.


git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@415 4aad255d-cdde-0310-9447-f3009e2ae8c0