Deprecate or remove mbstring function overloads in PHP 7

Hi internals! The mbstring extension supports replacing PHP string functions with multibyte variants through the mbstring.func_overload ini option. This ini setting is a real PITA for code compatibility, as it makes it impossible to rely on the output of even the most basic PHP functions, like strlen(). Security-critical code in libraries and frameworks typically handles this issue by conditionally using either strlen() or 8bit mb_strlen(). Apart from that, the issue is generally ignored. If we do not wish to drop support for this option in PHP 7, I would at least suggest to deprecate it. Thoughts? Nikita