Thanks to Evan_ for the report and Marco Buttu for the patch.

so let's defer this until 3.7, 3.8, ... all have this new function.

  - There was no real problem to begin with.

  - The hypothetical problem has been fixed by 5bdc8e1a50c8.

Python/random.c is more then in the 3.6 branch.

Copy and then adapt Python/random.c from default branch. Difference between 3.5
and default branches:

* Python 3.5 only uses getrandom() in non-blocking mode: flags=GRND_NONBLOCK
* If getrandom() fails with EAGAIN: py_getrandom() immediately fails and
  remembers that getrandom() doesn't work.
* Python 3.5 has no _PyOS_URandomNonblock() function: _PyOS_URandom()
  works in non-blocking mode on Python 3.5

In urllib.request, suffixes in no_proxy environment variable with
leading dots could match related hostnames again (e.g. .b.c matches a.b.c).
Patch by Milan Oberkirch.

maintenance issues (cost/benefit).

path in order to avoid maintenance issues.