Occurences: fix coordinates of indexing operators
Occurences: add support for constructors
Constructor occurence: limit location to constructor name
emacs: require iedit in merlin-iedit
Add Enclosing command
Which commands: allow multiple queries, ordered by priority

This allow falling back to "protocol.mli" when searching for
"protocol.ml" when only the ".mli" file exists, and vice versa.
emacs: implement similar fallback
Merge remote branch 'upstream/ocaml-402' into ocaml-402
emacs: add select enclosing command