Update MongoDB document limit to 16MB


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@330798 c90b9560-bf6c-de11-be94-00142212c4b1
Capitalize MB abbreviation for MongoCursor::dead()


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@330799 c90b9560-bf6c-de11-be94-00142212c4b1