magit-revert-buffers: don't use auto-revert-handler

`auto-revert-handler' does quite a few things we don't need, so instead
of using that just call `revert-buffer', `vc-find-file-hook' directly.

Backport of edf2b42ec6c1309402e62e3b307e1656c8f38680.
travis-ci: use generic

See https://github.com/travis-ci/travis-ci/issues/1201.
Merge branch 'master' into next

Conflicts:
	magit.el