in particular, there is no more need to define intermediate
sorts or to close the set of protected types wrt subtyping

You must run ./config.status after this commit

- create_env_of_loadpath is now provided in Env instead of Lexer
- find_channel functions now depend on format to determine the
  suitable extensions

thanks to Frédéric Herbreteau for the patch!

The TPTP plugin does not load (Linux 64bit) when compiled with
the Menhir library. For the moment, let us leave it as it is.
The use of the library is not necessary and is off by default.

in case of syntax error on reload, do not exit abruptly but displays a message and scroll to loc of the error

Makefile targets to build the gallery (to be discussed)