Runtime: fix caml_hash so that it can be optimized by Google Chrome
Runtime: fix caml_hash so that it can be optimized by Google Chrome

The JavaScript engine does not like integer multiplication by a 32-bit
unsigned integer, so explicitly convert the constants to 32-bit signed
integers.

OCamlPro-Henry/js_of_ocaml,alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml,alainfrisch/js_of_ocaml,OCamlPro-Henry/js_of_ocaml,OCamlPro-Henry/js_of_ocaml,OCamlPro-Henry/js_of_ocaml,OCamlPro-Henry/js_of_ocaml