Take into account the new distribution of files in new directories with new namespace :

 -  New options have been introduced: BUILD_XLEGACYSIMPLECUT and USE_XDOUBLECUT.
 -  remove use of MTL, ITL, PETSC, SPARSKIT and NONLINEARSOLVER (attic) and their options

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    Add boost system sequential control

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    Change comments in CMakeList.txt to clarify how variables <foe>_TEST are treated for:
           - atomic  tests (inside Xfiles),
           - general tests (inside Xtest ),
           - or both (because tests exist in both).