restore python 2.5/2.7.3 compatibility

PriorityQueue tests fail on 2.5 but this is to be expected.

```
$ python2.7 bin/testify test
..............WARNING  409 POST /results?runner=tries_twice (::1) 0.37ms
WARNING  409 POST /results?runner=tries_twice (::1) 0.31ms
ERROR    Skipping returning results for test test.plugins.http_reporter_test DummyTestCase.test because of error: error
...............................................ERROR    TestRunnerServer on port 0 has been asked to shutdown but its IOLoop is not running. Perhaps it died an early death due to discovery failure.
............................
PASSED.  89 tests / 51 cases: 89 passed, 0 failed.  (Total test time 1.27s)
```

```
$ python2.6 bin/testify test
..............WARNING  409 POST /results?runner=tries_twice (::1) 0.65ms
WARNING  409 POST /results?runner=tries_twice (::1) 0.61ms
ERROR    Skipping returning results for test test.plugins.http_reporter_test DummyTestCase.test because of error: error
...............................................ERROR    TestRunnerServer on port 0 has been asked to shutdown but its IOLoop is not running. Perhaps it died an early death due to discovery failure.
............................
PASSED.  89 tests / 51 cases: 89 passed, 0 failed.  (Total test time 3.25s)
bryce@sff7u6-254:~/Testify (bryce_273_compat)  14:21:06
```

```
$ python2.5 bin/testify test
..............WARNING  409 POST /results?runner=tries_twice (::1) 0.43ms
WARNING  409 POST /results?runner=tries_twice (::1) 0.51ms
ERROR    Skipping returning results for test test.plugins.http_reporter_test DummyTestCase.test because of error: error
...............................................ERROR    error: test.test_runner_server_test TestRunnerServerBrokenImportTestCase.test_reports_are_generated_after_discovery_failure
Traceback (most recent call last):
  File "./test/test_runner_server_test.py", line 80, in setup_server
    self.start_server()
  File "./test/test_runner_server_test.py", line 112, in start_server
    super(TestRunnerServerBrokenImportTestCase, self).start_server(test_reporters=[self.mock_reporter])
  File "./test/test_runner_server_test.py", line 57, in start_server
    plugin_modules=[],
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 128, in __init__
    self.test_queue = AsyncDelayedQueue()
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 31, in __init__
    self.data_queue = Queue.PriorityQueue()
AttributeError: 'module' object has no attribute 'PriorityQueue'

EERROR    Could not remove broken import file /Users/bryce/Testify/test/fake_broken_importMVwn_3.pyc: OSError(2, 'No such file or directory')
ERROR    error: test.test_runner_server_test TestRunnerServerTestCase.test_fail_then_timeout_twice
Traceback (most recent call last):
  File "./test/test_runner_server_test.py", line 80, in setup_server
    self.start_server()
  File "./test/test_runner_server_test.py", line 57, in start_server
    plugin_modules=[],
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 128, in __init__
    self.test_queue = AsyncDelayedQueue()
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 31, in __init__
    self.data_queue = Queue.PriorityQueue()
AttributeError: 'module' object has no attribute 'PriorityQueue'

EERROR    error: test.test_runner_server_test TestRunnerServerTestCase.test_get_next_test_doesnt_loop_forever
Traceback (most recent call last):
  File "./test/test_runner_server_test.py", line 80, in setup_server
    self.start_server()
  File "./test/test_runner_server_test.py", line 57, in start_server
    plugin_modules=[],
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 128, in __init__
    self.test_queue = AsyncDelayedQueue()
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 31, in __init__
    self.data_queue = Queue.PriorityQueue()
AttributeError: 'module' object has no attribute 'PriorityQueue'

EERROR    error: test.test_runner_server_test TestRunnerServerTestCase.test_passing_tests_run_only_once
Traceback (most recent call last):
  File "./test/test_runner_server_test.py", line 80, in setup_server
    self.start_server()
  File "./test/test_runner_server_test.py", line 57, in start_server
    plugin_modules=[],
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 128, in __init__
    self.test_queue = AsyncDelayedQueue()
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 31, in __init__
    self.data_queue = Queue.PriorityQueue()
AttributeError: 'module' object has no attribute 'PriorityQueue'

EERROR    error: test.test_runner_server_test TestRunnerServerTestCase.test_requeue_on_failure
Traceback (most recent call last):
  File "./test/test_runner_server_test.py", line 80, in setup_server
    self.start_server()
  File "./test/test_runner_server_test.py", line 57, in start_server
    plugin_modules=[],
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 128, in __init__
    self.test_queue = AsyncDelayedQueue()
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 31, in __init__
    self.data_queue = Queue.PriorityQueue()
AttributeError: 'module' object has no attribute 'PriorityQueue'

EERROR    error: test.test_runner_server_test TestRunnerServerTestCase.test_requeue_on_timeout
Traceback (most recent call last):
  File "./test/test_runner_server_test.py", line 80, in setup_server
    self.start_server()
  File "./test/test_runner_server_test.py", line 57, in start_server
    plugin_modules=[],
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 128, in __init__
    self.test_queue = AsyncDelayedQueue()
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 31, in __init__
    self.data_queue = Queue.PriorityQueue()
AttributeError: 'module' object has no attribute 'PriorityQueue'

EERROR    error: test.test_runner_server_test TestRunnerServerTestCase.test_timeout_then_fail_twice
Traceback (most recent call last):
  File "./test/test_runner_server_test.py", line 80, in setup_server
    self.start_server()
  File "./test/test_runner_server_test.py", line 57, in start_server
    plugin_modules=[],
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 128, in __init__
    self.test_queue = AsyncDelayedQueue()
  File "/Users/bryce/Testify/testify/test_runner_server.py", line 31, in __init__
    self.data_queue = Queue.PriorityQueue()
AttributeError: 'module' object has no attribute 'PriorityQueue'

E.....................
FAILED.  89 tests / 51 cases: 82 passed, 7 failed.  (Total test time 0.28s)
```