fail if ocamlfind is not installed

Summary:
public
We were testing for the wrong program here.

Reviewed By: dulmarod

Differential Revision: D2748990

fb-gh-sync-id: d2af6f6

configure.ac

@@ -39,7 +39,7 @@ AC_ASSERT_PROG([ocamlc], [$OCAMLC])
 AC_ASSERT_PROG([ocamlopt], [$OCAMLOPT])
 AC_ASSERT_PROG([ocamlbuild], [$OCAMLBUILD])
 AC_PROG_FINDLIB
-AC_ASSERT_PROG([findlib], [$FINDLIB])
+AC_ASSERT_PROG([ocamlfind], [$OCAMLFIND])
 AC_PROG_OCAMLLEX
 AC_ASSERT_PROG([ocamllex], [$OCAMLLEX])
 AC_PROG_OCAMLYACC