+Abella 2.0.2

Also removed abella.2.0.0, which is now obsolete
Abella 2.0.2 requires OCaml 4.01.0+
Sync latest compiler pull requests
Merge pull request #2931 from bactrian/sync-prs-1414105201

Sync OCaml compiler PRs
Merge pull request #2915 from chaudhuri/abella.2.0.2

+Abella 2.0.2
+mirage-xen-minios.0.4.1