restored l_tree
Support for OCaml 3.12: provide List.iteri
Support for OCaml 3.12: first class modules

Fix the following compiler error in Ocaml 3.12:

 * (value expr) not supported yet
fix: can evaluate a csv file whose column id's are different than feature id's, as long as they can be associated by name
Support for OCaml 3.12: more fixes
Merge branch 'eval-eat-your-own-dog-food'
Merge branch 'master' into distributed

Conflicts:
	learn.ml
	utils.ml
refined broadcast send/recv pattern