Support Python 3

[albertyw]

I get this when trying to run dbshell_plus:

./manage.py dbshell_plus
Traceback (most recent call last):
  File "./manage.py", line 12, in <module>
    execute_from_command_line(sys.argv)
  File "/home/albertyw/.virtualenvs/env/lib/python3.5/site-packages/django/core/management/__init__.py", line 363, in execute_from_command_line
    utility.execute()
  File "/home/albertyw/.virtualenvs/env/lib/python3.5/site-packages/django/core/management/__init__.py", line 355, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/albertyw/.virtualenvs/env/lib/python3.5/site-packages/django/core/management/__init__.py", line 205, in fetch_command
    klass = load_command_class(app_name, subcommand)
  File "/home/albertyw/.virtualenvs/env/lib/python3.5/site-packages/django/core/management/__init__.py", line 40, in load_command_class
    module = import_module('%s.management.commands.%s' % (app_name, name))
  File "/home/albertyw/.virtualenvs/env/lib/python3.5/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 986, in _gcd_import
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 661, in exec_module
  File "<frozen importlib._bootstrap_external>", line 767, in get_code
  File "<frozen importlib._bootstrap_external>", line 727, in source_to_code
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "/home/albertyw/.virtualenvs/env/lib/python3.5/site-packages/django_dbshell_plus/management/commands/dbshell_plus.py", line 23
    except OSError, e:
                  ^
SyntaxError: invalid syntax