Fix "Disallowed Key Characters" — core CodeIgniter

[nfreear]

Applies to approval server on .open.ac.uk network, with OU cookies, etc. ... ;)

• https://stackoverflow.com/questions/29744740/disallowed-key-characters-codeigniter-error
• https://github.com/IET-OU/cloudengine/blob/master/system/libraries/Input.php#L217;

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• — Mark as //ou-specific

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