- do not add to the new namespace the old instantiated names
- namespaces with the same name are merged instead of raising
  an exception.

Attention: examples clash_namespace1.why, already_theory1.why,
already_theory2.why, clash_type6.why, clash_type7.why migrated 
from bench/typing/bad/ to bench/typing/good/. Please, consult
these files and make sure you comprehend and approve the new
semantics.

   driver.ml : Rattrape TheoriesNotFound
   bench.in : Test jusqu'au bout les drivers
   drivers : corrige le nom des théories
   
TODO modifier driver_parser pour prendre (+) au lieu de (_+_)