Extracted inline code to permanent files
Python3 compatibility of test files
tests.run_python: new_tmp flag to create new temporary directory and
    pass it to child process via environ[TMP].
    The directory with any files is removed when child process is
    finished.
tests.rmtree: silent version of shutil.rmtree()

This patch consists of the following changes:

* Splitting eventlet.greenio into base, py2 and py3 parts
  (eventlet.greenio should be exporing the same public objects). This
  change is motivated by the size and the number of conditions present
  in the current greenio code
* Connected to the first point: implementing almost completely new
  GreenPipe callable utilizing parts of old GreenPipe code but dropping
  _fileobject/SocketIO inheritance in favour of io.FileIO and making use
  of patched _pyio.open function which wraps raw file-like object in
  various readers and writers (they take care of the buffering,
  encoding/decoding etc.)
* Implementing (from scratch or updating existing versions)
  green versions of the following modules:

  * http.* (needed by Python 3's urllib)
  * selectors (Python >= 3.4, used in subprocess module)
  * urllib.* (needed by various tests and we were already exposing green
    urllib)

* Modifying some tests to make tests pass, which includes:

  * unicode/bytestring issues
  * modifying wsgi_test_conntimeout.py to not pass bufsize and close
    arguments to ExplodingSocketFile - on Python 3 it inherits from
    SocketIO, which doesn't deal with buffering at all as far as I can
    see

* Random cleaning up and reorganizing
* Requiring Python 3.x tests to pass for the whole build to pass

Known issues:

* code repetition
* naming inconsistencies
* possibly breaking some external code using private eventlet.greenio attributes

Closes https://github.com/eventlet/eventlet/issues/108

Affects https://github.com/eventlet/eventlet/issues/6 (I'd call it an
experimental support)

Should help for https://github.com/eventlet/eventlet/issues/145
Should help for https://github.com/eventlet/eventlet/issues/157

The importlib module must use real thread locks, not eventlet.Semaphore.

This includes changes to WSGI, websocket, bytes/str/unicode handling,
SSL, backdoor, greenio and tests.

Some comments and conditionals (PY2/PY3) were added for clarity

GH issues:

Closes #106
Closes #111
Closes #118
Closes #141

Incidentally should also close #135 (reopen if didn't)

cc #6

https://github.com/eventlet/eventlet/issues/101

For now, pep8 check is only run for some files known to be clean,
we should clean the rest and enable pep8 check for all files then.

https://github.com/eventlet/eventlet/pull/59

Proposal is to use it for new subprocess tests where module is commited to repo