Python 3 test fails

Currently Python 3 tests fail like this:
```
$ python3.4 setup.py test
running test
running egg_info
writing dependency_links to ginga.egg-info/dependency_links.txt
writing ginga.egg-info/PKG-INFO
writing requirements to ginga.egg-info/requires.txt
writing top-level names to ginga.egg-info/top_level.txt
reading manifest file 'ginga.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
writing manifest file 'ginga.egg-info/SOURCES.txt'
running build_ext
Traceback (most recent call last):
  File "setup.py", line 69, in <module>
    cmdclass={'build_py': build_py}
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/distutils/dist.py", line 955, in run_commands
    self.run_command(cmd)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/distutils/dist.py", line 974, in run_command
    cmd_obj.run()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/setuptools/command/test.py", line 142, in run
    self.with_project_on_sys_path(self.run_tests)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/setuptools/command/test.py", line 122, in with_project_on_sys_path
    func()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/setuptools/command/test.py", line 163, in run_tests
    testRunner=self._resolve_as_ep(self.test_runner),
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/main.py", line 92, in __init__
    self.parseArgs(argv)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/main.py", line 139, in parseArgs
    self.createTests()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/main.py", line 146, in createTests
    self.module)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/loader.py", line 146, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/loader.py", line 146, in <listcomp>
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/loader.py", line 117, in loadTestsFromName
    return self.loadTestsFromModule(obj)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/setuptools/command/test.py", line 37, in loadTestsFromModule
    tests.append(self.loadTestsFromName(submodule))
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/loader.py", line 105, in loadTestsFromName
    module = __import__('.'.join(parts_copy))
  File "/Users/deil/code/ginga/ginga/tests/test_ImageView.py", line 5, in <module>
    from ginga import ImageView, AstroImage
  File "/Users/deil/code/ginga/ginga/ImageView.py", line 17, in <module>
    from ginga.misc import Callback, Settings
  File "/Users/deil/code/ginga/ginga/misc/Callback.py", line 74
    except Exception, e:
                    ^
SyntaxError: invalid syntax
```