fix test runner and pyximport in Py 2.7.9 and 3.4+: setuptools replaces "distutils.dist.Distribution" *after* we import it, which then breaks the input validation in "distutils.cmd"

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extra : transplant_source : %3A%84%AC%02E%17%D8%EE%E64Mpv%25%A3%8E%8B%E5%CA%19
postpone import of distutils Extension type in test runner in case setuptools gets imported in between

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extra : transplant_source : %9B%C2%08Q%DDt%9A%99%A4%CAK%5D%8F%3A%A9%E4F%19%96%CD
changelog
merge 0.21.x branch into master