mb_convert_variables()
mb_convert_variables()

- fixes https://github.com/peachpiecompiler/peachpie/issues/461
- cleanups some mb internal code

peachpiecompiler/peachpie,iolevel/peachpie-concept,peachpiecompiler/peachpie,peachpiecompiler/peachpie,iolevel/peachpie,iolevel/peachpie-concept,iolevel/peachpie,iolevel/peachpie-concept,iolevel/peachpie