constrain cowabloga to latest cohttp
restrict facebook-sdk to cohttp<0.12.0
restrict irmin to cohttp<0.12.0
restrict opium to cohttp<0.12.0

see rgrinberg/opium#14
restrict vhd-tool to cohttp<0.12.0
restrict xen-api-client to older cohttp only
remove an excess cohttp constraint
added ppx_overload.1.0.1
lwt.2.4.3 doesnt compile on ocaml>=4.02.0
core 111.28.01
Fix unavailability checking on opam 1.1.1. Fix #3021.
Merge pull request #3023 from dsheets/opam-1.1-availability-travis

Fix unavailability checking on opam 1.1.1. Fix #3021.
quickcheck.1.0.2
Merge pull request #3024 from domsj/quickcheck-1.0.2

quickcheck.1.0.2
Sync latest compiler pull requests
Merge pull request #3025 from bactrian/sync-prs-1415318401

Sync OCaml compiler PRs
Added frame-pointer variant of OCaml 4.02.1
Merge pull request #3027 from Leonidas-from-XIV/feature/4.02.1+fp

Added frame-pointer variant of OCaml 4.02.1
restrict message-switch to cohttp <0.12.0
restrict websocket to cohttp <0.12.0