fix almost all warnings

.ocaml-config.sh

.travis.yml

dune-project

lustrec.opam

opam.in

src/automata.ml

src/backends/Ada/ada_backend.ml

src/backends/Ada/ada_backend_adb.ml

src/backends/Ada/ada_backend_ads.ml

src/backends/Ada/ada_backend_common.ml

src/backends/Ada/ada_backend_wrapper.ml

src/backends/Ada/misc_lustre_function.ml

src/backends/C/c_backend.ml

src/backends/C/c_backend_common.ml

src/backends/C/c_backend_header.ml

src/backends/C/c_backend_main.ml

src/backends/C/c_backend_makefile.ml

src/backends/C/c_backend_mauve.ml

src/backends/C/c_backend_spec.ml

src/backends/C/c_backend_src.ml