squashed a whole bunch of PRs

closes #1907
closes #1908
closes #1909
closes #1910
closes #1911
closes #1912
closes #1913
closes #1914
closes #1915
closes #1916
closes #1917
closes #1918
closes #1919
closes #1920
closes #1921
closes #1922

actually we could right now. but I don't like to introduce that change in
a feature branch.

We still need 5 to test on old php versions, but travis uses 6 for newer
PHP versions (and 5 may break on those).

Luckily both versions aren't that far apart, yet. This adds a thin
adapter class when running on 6.

See for reference #1837 and sebastianbergmann/phpunit#2503

However those classes are already supported in PHP 5.7 so we can switch
to them without breaking backward-compatibility.

The documentation says sessionIDs are between 22 and 256 chars long. A
quick test only showed 26 chars in common configurations, but this
should cover all possibilities.

When an invalid session ID is passed to PHP a warning is thrown, but the
session is still initialized with this invalid ID (throwing additional
warnings on save).

This makes sure such invalid IDs are removed from the cookie array
before initializing the session.

PHP bug references:

https://bugs.php.net/bug.php?id=68063
https://bugs.php.net/bug.php?id=73860

This partly fixes #1883

Translation update (zh)

Translation update (zh)

Translation update (nl)

Otherwise the it will fail with the following error:

	2017/02/20 14:34:57 [error] 16242#0: *59 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Call to undefined function random_int() in /var/www/dokuwiki/inc/PassHash.class.php on line 630" while reading response header from upstream, client: 172.18.35.245, server: _, request: "POST /dokuwiki/install.php HTTP/1.1", upstream: "fastcgi://unix:/var/run/php-fpm/php-fpm.sock:", host: "10.5.234.170", referrer: "http://10.5.234.170/dokuwiki/install.php"

Fixes #1852

The check did not work any more. see #1853

direction is always ltr for russian

Merge branch 'lang_update_274' of git://github.com/dokuwiki-translate/dokuwiki into pull-request-1847

* 'lang_update_274' of git://github.com/dokuwiki-translate/dokuwiki:
  translation update

Translation update (nl)

Translation update (it)