Upgrade to OCaml 4.08+beta2

[jhwoodyatt]

For reference, this is what OCaml 4.08+beta2 seems to require (issue #69).

[jhwoodyatt]

I don't understand why Travis CI is complaining, and I don't have the time to investigate.

[hhugo]

cc @xclerc

[kit-ty-kate]

@jhwoodyatt I opened a PR on your fork to fix travis: jhwoodyatt#1

[kit-ty-kate]

all green. cc @alainfrisch @gasche (not sure who's maintaining this)

[gasche]

I know I'm not, but maybe I can try to have a look later in the week if nobody has stepped up. (cc @alainfrisch @nojb @xclerc @diml)

[nojb]

LGTM. I don't have merge rights though.

[gasche]

It's embarrassing that I don't know how to check the list of people with merge rights (to me or to the Github interface), but it may be that only @alainfrisch is in this set. I would warmly recommend to add @nojb to it, though :-)

[Drup]

I have merge rights! But I can't add more people to the repository.
I also have very little time right now, so I won't be able to make a release myself for a few weeks.

[gasche]

While testing the master branch on 4.08 I found a small issue -- the generated code still mentions Pervasives -- for which I propose a fix in #72. Would someone look at it and consider merging it?

[XVilka]

Shouldn't be this merged one already? It is pretty obvious it is good one.

[hhugo]

I believe metaquot is currently broken with this feature.
One should ignore pexp_loc_stack, ptyp_loc_stack, ppat_loc_stack when generating patterns on the ast. see what's done for location and attributes: https://github.com/ocaml-ppx/ppx_tools/blob/master/ppx_metaquot.ml#L175

Also see the patch in ppx_tools_versionned https://github.com/ocaml-ppx/ppx_tools_versioned/pull/22/files#diff-7ab097557bb7183454f885e4595acc38R180