Merlin v1.7.1 bugfix release

v1.7 vim-mode install script relied on a GNU tool, it didn't work for BSDs users
Update ocaml-version constraints on all merlin
Add merlin 2 prerelease for 4.02
merlin.2 -> merlin.2.0.0
merlin.2.0.0: remove upperbound on ocaml-version
Merge pull request #2484 from def-lkb/master

Merlin v1.7.1 bugfix release