New options --coq-lib-path and --coq-lib-no-path control this behavior.

Makefile fix: when determining whether the suffix `.exe` should be used, test whether the OS is Windows, not whether the compiler is MSVC.

of menhir --suggest-ocamlfind, so that the Makefile works when
Menhir is compiled as a Windows executable. (Suggested by Jonathan
Protzenko.)

bindings of the form [x = $i] for ocamlyacc. This should work around a
name capture caused by the fact that ocamlyacc internally translates
[$i] to [_i] (and our own variables are often of the form [_i]).

%type declarations for ocamlyacc. (Reported by Kenji Maillard.)