Lots of FIXMEs and the routing isn't integrated, yet

This is neither complete nor working, yet

Those tests either just check that an exception is NOT thrown or are
there to check dependencies for other tests. Newer phpunits mark all
tests as risky that have no assertion.

I supplemented the existing comments on the methods in which there was not enough information to the standard phpDoc.

I supplemented the existing comments on the methods in which there was not enough information to the standard phpDoc.

I supplemented the existing comments on the methods in which there was not enough information to the standard phpDoc.

I supplemented the existing comments on the methods in which there was not enough information to the standard phpDoc.

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

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