+Abella 2.0.2

Also removed abella.2.0.0, which is now obsolete
Abella 2.0.2 requires OCaml 4.01.0+
travis: Fix the check for package availability on older opams

turns out there used to be no good way of simply checking this, so I'm just trying to
install with --dry-run and expecting an empty stdout if the package is unavailable
vastly reduce the number of osx tests to reduce the worker backlog
Fix ocaml-version constraint on ppx_tools again.
Merge pull request #2942 from whitequark/fix-ppx_tools

Fix ocaml-version constraint on ppx_tools again
core 112.01.01
add ojs-base 0.2.0
cow.0.8.1: restrict to ocaml < 4.02 per mirage/ocaml-cow#48
added OCamltter 3.0.0
Add mpris.0.1.0

Signed-off-by: John Else <john.else@citrix.com>
add stog 0.14.0
Merge pull request #2946 from johnelse/add-mpris.0.1.0

Add mpris.0.1.0
commit to enforce re-Travis
Merge branch 'master' of https://github.com/OCamlPro/opam-repository
fixed dependency
Remove unstable mirage-www package from the main repo
Merge pull request #2949 from samoht/mirage-www

Remove unstable mirage-www package from the main repo
travis: fix new opam with old compiler availability check
Merge pull request #2951 from dsheets/abella-and-travis

Fix the travis script for new opams with older compilers