simplify the spellcheck functions

- expose the core spellchecking functionality in Misc rather than Typetexp
- remove the too high-order (yet insufficiently parametric)
  Typetexp.spellcheck from the public interface
- rewrite the spellchecking functions for variants and fields in
  Typecore from the Misc functions rather than reusing
  Typetexp.spellcheck

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15650 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
'Did you mean' for variables missing on one side of an or-pattern

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15651 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
simplify spellchecking of labels in typecore.ml:

By computing the list of valid names at Wrong_name raising point, we
can remove the logic to reconstruct the set of valid names to draw
suggestion from after the fact:
- no spellchecking-related code in the NameChoice functor
- seamlessly extends to fields of inline records (were not spellchecked before)

I made the type of the "wrong name" in the Wrong_name exception more
precise, from Longident.t to string. The rationale is that:
- we only raise this exception when the longident happens to be
  a (Lident str)
- the list of valid names is a list of field or variant names; those
  are strings rather than idents

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15652 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
typecore.ml: minor refactoring

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15653 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
'Did you mean' for unbound method names

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15654 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
'Did you mean' for instance variables

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15655 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02