Avoid crash caused by missing "id" attribute

I have no idea if this is the correct fix, but it avoids the below crash. (I would file a bug report instead, but I don't feel like logging into Launchpad.)

```bash
$ pyflakes autoflake.py
Traceback (most recent call last):
  File "/Users/myint/Library/Python/3.3/bin/pyflakes", line 9, in <module>
    load_entry_point('pyflakes==0.6.2a0', 'console_scripts', 'pyflakes')()
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/api.py", line 129, in main
    warnings = checkRecursive(args, reporter)
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/api.py", line 120, in checkRecursive
    warnings += checkPath(sourcePath, reporter)
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/api.py", line 79, in checkPath
    return check(f.read() + '\n', filename, reporter)
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/api.py", line 58, in check
    w = checker.Checker(tree, filename)
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/checker.py", line 239, in __init__
    self.runDeferred(self._deferredFunctions)
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/checker.py", line 275, in runDeferred
    handler()
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/checker.py", line 693, in runFunction
    self.handleNode(stmt, node)
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/checker.py", line 527, in handleNode
    handler(node)
  File "/Users/myint/Library/Python/3.3/lib/python/site-packages/pyflakes-0.6.2a0-py3.3.egg/pyflakes/checker.py", line 768, in TRY
    handler_names.append(exc_type.id)
AttributeError: 'Attribute' object has no attribute 'id'
$ pyflakes  --version
0.6.2a0
```