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
magit-section-show-headings-1: always set HIDDEN slot to nil

This prevents `magit-section-cycle' from
getting stuck in the "show headings" state.
magit-diff-wash-revision: wrap complete header in section

Wrap the complete header, including header lines, commit message and
diffstat in the header section.  This allows hiding everything except
for the diffs in one step.
magit-section-show-headings-1: cosmetics
README.md: fix tarball url
magit-revert-buffers: run magit-revert-buffer-hook again
magit-revert-buffers: "reverts" all file-visiting buffers again

This is a temporary kludge, on next I have to find a better solution.
See #1546.
magit-revert-buffers: compare truenames

See #1545.
Merge branch 'master' into next

Conflicts:
	README.md
	magit.el