API Disable discontinued Google Spellcheck in TinyMCE

Replaced by browser-based spellchecking if available (Chrome, Firefox),
with instructions on how to use PSpell as an alternative.
Validate 'archiveDate' user data in Versioned

Not a security issue as such, since the user input is sanitized
before being used in Versioned->augmentSQL(). But it shouldn't
reach the session state either, since that's commonly assumed
to be sanitized data, and it leaves unnecessary room for error.

strtotime() has fairly loose validation rules around dates,
but its a good "first line of defence".
BUG Fixing installer not checking display_errors correctly.

Fixes issue #2479. Installer sets display_errors on, but it checks
the changed value and not the original one set in php.ini.
Merge pull request #2328 from chillu/pulls/versioned-archivemode-validation

Validate 'archiveDate' user data in Versioned
Merge pull request #2288 from chillu/pulls/browser-spellcheck

API Disable discontinued Google Spellcheck in TinyMCE (#2213)
Merge pull request #2487 from halkyon/installer_error_check_30

BUG Fixing installer not checking display_errors correctly.
BUG Fixed cross-platform issues with test cases and file utilities
Merge pull request #2488 from tractorcow/pulls/3.0-platform-compatibility

BUG 3.0 Fixed cross-platform issues with test cases and file utility
Added 3.0.8 changelog
Removed link to non-functional dokuwiki install
Merge remote-tracking branch 'origin/3.0' into 3.1

Conflicts:
	dev/install/install.php5
	docs/en/index.md
	tests/core/CoreTest.php