Add file type checking

The check is made through loadMesh, but it has to be done also in geo()
for the case where geo is used outsides of the importer.
(for example for geo descriptor modifications)
Merge branch 'develop' of github.com:feelpp/feelpp into develop
Merge branch 'develop' of github.com:feelpp/feelpp into develop
up c++11 norm
Merge branch 'develop' of github.com:feelpp/feelpp into develop