Rollback PyPy3, add changenotes, enable other builds

PyPy3-3.5-5.7.1-beta has issues in the traceback
library (https://travis-ci.org/gevent/gevent/jobs/219394025):

  During handling of the above exception, another exception occurred:

  Traceback (most recent call last):
    File "/home/travis/build/gevent/gevent/src/greentest/greentest.py", line 297, in wrap_restore_handle_error
      return method(self, *args, **kwargs)
    File "/home/travis/build/gevent/gevent/src/greentest/greentest.py", line 169, in wrap_timeout
      return method(self, *args, **kwargs)
    File "test__event.py", line 146, in test_set_exception
      self.assertRaises(greentest.ExpectedException, s1.get)
    File "/home/travis/.runtimes/versions/pypy3.5_571/lib-python/3/unittest/case.py", line 728, in assertRaises
      return context.handle('assertRaises', args, kwargs)
    File "/home/travis/.runtimes/versions/pypy3.5_571/lib-python/3/unittest/case.py", line 177, in handle
      callable_obj(*args, **kwargs)
    File "/home/travis/.runtimes/versions/pypy3.5_571/lib-python/3/unittest/case.py", line 201, in __exit__
      traceback.clear_frames(tb)
    File "/home/travis/.runtimes/versions/pypy3.5_571/lib-python/3/traceback.py", line 216, in clear_frames
      tb.tb_frame.clear()
  AttributeError: 'Frame' object has no attribute 'clear'

Fixes #958

[skip appveyor]

.travis.yml

@@ -10,16 +10,16 @@ env:
     matrix:
       # These are ordered to get as much diversity in the
       # first group of parallel runs (4) as posible
-      #- TASK=test-py27-noembed
+      - TASK=test-py27-noembed
       - TASK=test-pypy
-      #- TASK=test-py36
-      #- TASK=lint-py27
+      - TASK=test-py36
+      - TASK=lint-py27
       - TASK=test-pypy3
-      #- TASK=test-py35
-      #- TASK=test-py278
-      #- TASK=test-py27
-      #- TASK=test-py34
-      #- TASK=test-py27-cffi
+      - TASK=test-py35
+      - TASK=test-py278
+      - TASK=test-py27
+      - TASK=test-py34
+      - TASK=test-py27-cffi
 
 matrix:
   fast_finish: true

CHANGES.rst

@@ -9,6 +9,9 @@
 
 - Testing on Python 3.5 now uses Python 3.5.3 due to SSL changes. See
   :issue:`943`.
+- Linux CI has been updated from Ubuntu 12.04 to Ubuntu 14.04 since
+  the former has reached EOL.
+- Linux CI now tests on PyPy2 5.7.1, updated from PyPy2 5.6.0.
 - Python 2 sockets are compatible with the ``SOCK_CLOEXEC`` flag found
   on Linux. They no longer pass the socket type or protocol to
   ``getaddrinfo`` when ``connect`` is called. Reported in :issue:`944`

Makefile

@@ -110,7 +110,7 @@ PY34=$(BUILD_RUNTIMES)/snakepit/python3.4.5
 PY35=$(BUILD_RUNTIMES)/snakepit/python3.5.3
 PY36=$(BUILD_RUNTIMES)/snakepit/python3.6.0
 PYPY=$(BUILD_RUNTIMES)/snakepit/pypy571
-PYPY3=$(BUILD_RUNTIMES)/snakepit/pypy3.5_571
+PYPY3=$(BUILD_RUNTIMES)/snakepit/pypy3.3_5.5
 
 TOOLS=$(BUILD_RUNTIMES)/tools
 
@@ -181,7 +181,7 @@ test-pypy: $(PYPY)
 	PYTHON=$(PYPY) PIP=pip PATH=$(BUILD_RUNTIMES)/versions/pypy571/bin:$(PATH) make develop toxtest
 
 test-pypy3: $(PYPY3)
-	PYTHON=$(PYPY3) PIP=pip PATH=$(BUILD_RUNTIMES)/versions/pypy3.5_571/bin:$(PATH) make develop toxtest
+	PYTHON=$(PYPY3) PIP=pip PATH=$(BUILD_RUNTIMES)/versions/pypy3.3_5.5/bin:$(PATH) make develop toxtest
 
 test-py27-cffi: $(PY27)
 	GEVENT_CORE_CFFI_ONLY=1 PYTHON=python2.7.13 PATH=$(BUILD_RUNTIMES)/versions/python2.7.13/bin:$(PATH) make develop toxtest

scripts/install.sh

@@ -106,7 +106,7 @@ for var in "$@"; do
       install pypy2-5.7.1 pypy571
       ;;
     pypy3)
-      install pypy3.5-5.7.1-beta pypy3.5_571
+      install pypy3.3-5.5-alpha pypy3.3_5.5
       ;;
   esac
 done