Fixed pin_advanced+http
Marking big-upgrade whith internal solver as an expected failure (again)

See
https://github.com/ocaml/opam/commit/f06cefa587b8f7369dc72b967cb83ad9064d71e4#commitcomment-7062754
this way we can at least start running travis with the internal solver.
Merge pull request #40 from AltGr/internal-solver

Re-enabling big-upgrade expected failure