Add revision display tests and fix issues

[phy25]

This is a more well-organized patch replacing PR #98, after tests are split and carefully compared between code branches.

To sum up what these commits do:

1. Add basic "show expected version" tests. They were written based on definitions at https://www.dokuwiki.org/plugin:publish#display_revision. And it failed because:

There were 2 failures:

1. approvel_test::test_show_expected_revision Visiting a draft revision with AUTH_READ did not return draft content. Failed asserting that false is true. /home/travis/build/phy25/dokuwiki-plugin-publish/lib/plugins/publish/_test/publish.test.php:267
2. approvel_test::test_show_expected_revision_hide_drafts Visiting a draft revision with hide_drafts on did not return in denied mode. Failed asserting that false is true. /home/travis/build/phy25/dokuwiki-plugin-publish/lib/plugins/publish/_test/publish.test.php:286

FAILURES! Tests: 36, Assertions: 104, Failures: 2.

2. Fix "visiting a draft revision with AUTH_READ did not return draft content", In the test case it is showing the latest version (redirected). So don't redirect to the latest revision if [specific] [draft] revision is requested. After these commits, tests error reduced:

There was 1 failure:

1. approvel_test::test_show_expected_revision_hide_drafts Visiting a draft revision with hide_drafts on did not return in denied mode. Failed asserting that false is true. /home/travis/build/phy25/dokuwiki-plugin-publish/lib/plugins/publish/_test/publish.test.php:286

FAILURES! Tests: 36, Assertions: 104, Failures: 1.

3. Fix "visiting a draft revision with hide_drafts on did not return in denied mode". Here we have to detect user permission based on REV instead of ID, because of the "hide drafts" feature. The code is somewhat inefficient indeed because I tried to keep consistence of the function usage in old parts of the code, so this may be optimized later. Whatever, it works.

OK (36 tests, 105 assertions)

[phy25]

Without this PR the tests will always fail now, in 2019. I don't quite remember why I mixed a lot of other non-essential bugfix into this PR, but please review this when you have time. Thanks!

[phy25]

There's an issue after applying this patch: with $conf['plugin']['publish']['hide drafts'] = 1;$conf['plugin']['publish']['author groups'] = 'admin';, when a user out of author groups with edit permission looks at a page with currently not-approved version and previous approved version, it doesn't show the approved version, but showing denied message instead.

It might be because handle_start redirect code won't handle requests from users with edit access.

https://github.com/cosmocode/dokuwiki-plugin-publish/blob/2537e35e66461bd9936bf474631e5d72cc285136/action/start.php#L34-L36

A previous commit shows that this line makes redirect "apply to readers only". Honestly I suddenly don't know what to do with so many unclear behavior from this plugin.