Document callback signatures

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Prefer anonymous function over create_function()

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@330241 c90b9560-bf6c-de11-be94-00142212c4b1
Fix extension-membership

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@330242 c90b9560-bf6c-de11-be94-00142212c4b1
Document set_error_handler(null)

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