Handle filenames that can't be decoded to unicode.

Another Python2 specific case to handle.

traceback2/__init__.py

@@ -380,7 +380,7 @@ class StackSummary(list):
         for frame in self:
             row = []
             row.append(u('  File "{0}", line {1}, in {2}\n').format(
-                frame.filename, frame.lineno, frame.name))
+                _some_str(frame.filename), frame.lineno, frame.name))
             if frame.line:
                 row.append(u('    {0}\n').format(frame.line.strip()))
             if frame.locals:

traceback2/tests/test_traceback.py

@@ -605,6 +605,16 @@ class TestStack(unittest.TestCase):
             ['  File "foo.py", line 1, in fred\n    line\n'],
             s.format())
 
+    def test_format_bad_filename(self):
+        # Filenames in Python2 may be bytestrings that will fail to implicit
+        # decode.
+        # This won't decode via the implicit(ascii) codec.
+        fname = u('\u5341').encode('shift-jis')
+        s = traceback.StackSummary.from_list([(fname, 1, 'fred', 'line')])
+        self.assertEqual(
+            ['  File "b\'\\x8f\\\\\'", line 1, in fred\n    line\n'],
+            s.format())
+
     def test_locals(self):
         linecache.updatecache('/foo.py', globals())
         c = test_code('/foo.py', 'method')
@@ -627,7 +637,7 @@ class TestStack(unittest.TestCase):
                 traceback.walk_stack(None), capture_locals=True, limit=1)
         s = some_inner(3, 4)
         self.assertEqual(
-            ['  File "' + FNAME + '", line 627, '
+            ['  File "' + FNAME + '", line 637, '
              'in some_inner\n'
              '    traceback.walk_stack(None), capture_locals=True, limit=1)\n'
              '    a = 1\n'