Rtree : cleanup of the comparing code

 * Using generic fold functions was unecessarily obscure
 * No more List.mem and hence indirect use of ocaml generic comparison
 * Rtree.equiv (former Rtree.compare_rtree) has now a less cryptic
   semantic...

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16934 85f007b7-540e-0410-9357-904b9bb8a0f7
inductive.ml : get rid of some obvious (Lazy.force (lazy t))

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16935 85f007b7-540e-0410-9357-904b9bb8a0f7
More monomorphic List.mem + List.assoc + ...

 To reduce the amount of syntactic noise, we now provide
 a few inner modules Int.List, Id.List, String.List, Sorts.List
 which contain some monomorphic (or semi-monomorphic) functions
 such as mem, assoc, ...

 NB: for Int.List.mem and co we reuse List.memq and so on.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16936 85f007b7-540e-0410-9357-904b9bb8a0f7