MenhirLib remains under LGPL with a linking exception.
MenhirSdk is considered part of the Generator.
Updated the header of every source file under version control.

a parser produced by menhir --table cannot be linked with an incorrect
version of MenhirLib.

so that the demos can be built properly, and uninstalls it
afterwards. Also, it checks that MenhirLib is not initially
installed already.

make local: transmit PATH.
make unlocal: new feature.

For the modules in MenhirLib, adopt the convention that the first letter of the file name must be capitalized.

Also, compile Menhir in $$TEMPDIR/$(PACKAGE), not $(PACKAGE).

So we have a better chance of success if new warnings appear.