Represent the closed flag of Ptyp_variant using closed_flag instead of bool, and start documenting the Parsetree.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13517 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Typo.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13518 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Document patterns.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13519 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02