setup: don't support py 3.5.0, 3.5.1, 3.5.2 because of bug in codecs
codecs.escape_encode() raises SystemError if an empty bytestring is passed. We
do that at some places in our code and because of this bug, things break.
Therefore we can't support the mentioned version. The bug was fixed in 3.5.3,
3.6.0 beta 2. We can't support 3.6.0 anyway because of bug in formatting
bytestrings.
Link to the python bug: https://bugs.python.org/issue25270
Differential Revision: https://phab.mercurial-scm.org/D4475