travis: known_failures: add test__issue6.py

It often fails with:

master ~/work/gevent $ python greentest/test__issue6.py
Traceback (most recent call last):
  File "greentest/test__issue6.py", line 11, in <module>
    assert err == '', (out, err, code)
AssertionError: ('11 chars.\n', 'Unhandled exception in thread started by \nsys.excepthook is missing\nlost sys.stderr\n', 0)
pep8 fixes
testrunner.py: fix syntax on py3
fix spurious failures in test__socket_dns6.py
remove unused imports
pyflakes fixes
disable tests in test_httpserver failing on 2.6

only on travis:

test_authorization (__main__.CGIHTTPServerTestCase) ... Traceback (most recent call last):
    File "/usr/lib/python2.6/CGIHTTPServer.py", line 255, in run_cgi
      os.execve(scriptfile, args, os.environ)
  OSError: [Errno 13] Permission denied
  FAIL
  test_headers_and_content (__main__.CGIHTTPServerTestCase) ... Traceback (most recent call last):
    File "/usr/lib/python2.6/CGIHTTPServer.py", line 255, in run_cgi
      os.execve(scriptfile, args, os.environ)
  OSError: [Errno 13] Permission denied
  FAIL
  test_invaliduri (__main__.CGIHTTPServerTestCase) ... ok
  test_post (__main__.CGIHTTPServerTestCase) ... Traceback (most recent call last):
    File "/usr/lib/python2.6/CGIHTTPServer.py", line 255, in run_cgi
      os.execve(scriptfile, args, os.environ)
  OSError: [Errno 13] Permission denied
  FAIL

  ======================================================================
  FAIL: test_get (__main__.SimpleHTTPServerTestCase)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "test_httpservers.py", line 242, in test_get
    File "test_httpservers.py", line 218, in check_status_and_reason
  AssertionError: 200 != 404

  ======================================================================
  FAIL: test_authorization (__main__.CGIHTTPServerTestCase)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "test_httpservers.py", line 349, in test_authorization
  AssertionError: ('Hello World\n', 'text/html', 200) != ("Exception happened during processing of request from ('127.0.0.1', 60525)\n----------------------------------------\n", None, 200)

  ======================================================================
  FAIL: test_headers_and_content (__main__.CGIHTTPServerTestCase)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "test_httpservers.py", line 330, in test_headers_and_content
  AssertionError: ('Hello World\n', 'text/html', 200) != ("Exception happened during processing of request from ('127.0.0.1', 38970)\n----------------------------------------\n", None, 200)

  ======================================================================
  FAIL: test_post (__main__.CGIHTTPServerTestCase)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "test_httpservers.py", line 337, in test_post
  AssertionError: "Exception happened during processing of request from ('127.0.0.1', 45146)\n----------------------------------------\n" != '1, python, 123456\n'
new travis build

- do pep8 and pyflakes checks
- do not tests examples with dependencies (psycopg2_pool.py, web.py, geventsendfile.py)
- do check -dbg build
- install cython from ppa
- drop 2.5, add 3.3 (currently fails)

new make commands:
 - make whitespace
 - make pep8
 - make pyflakes
 - make lint       # runs all of the above
 - make travis     # runs on travis

The linters are run first to abort broken builds early.

Removed --full option to testrunner.py, it is no longer needed.
travis: disable email notifications
os.py: do not import gevent.socket

since gevent.os is imported in __init__.py this makes gevent.socket imported in __init__.py which was never the intention.
subprocess.py: avoid reinitilization of rawlink()
update util/pyflakes.py

the subprocess.py warning was actually legit and was fixed in 47f1c3d581e98834224bdd28e8afe03e7cc16fae
travis: On Python3 use python3-version of pep8 #38

Previously pep8 and pyflakes were installed using the default system Python.
This changes 'make travis' to use the current Python version for those scripts as well.
This affects pep8, at least: on Python3 it complains about space in `print (...)`.
util/pyflakes.py: do not ignore errors, py3&py2.6

- do not swallow syntax errors
- make pyflakes.py py3-compatible #38
- run using specific version of python (previously pyflakes from the default python
  was used, which caused it to ignore py3-specific and py2.6-specific syntax errors
fix syntax of xtest_signal.py on python2.6
upgrade libev to 4.15

This should fix #361.
ares.pyx: add 'cdef basestring'
Fix links for examples (docs gevent servers)
Port gevent vfd to win64

Since long on win64 is 32-bit it cannot hold all possible
SOCKET handle values, making it theoretically possible to
get an exception "OverflowError: Python int too large to
convert to C long" if socket handles become too big. Now
on win64 it properly uses PY_LONG_LONG.
test___monkey_patching.py: don't fail if no tests are available for this version