traceback information is wrongly encoded.
Steps to reproduce:
1. Use a version of Windows that supports CP936 (Simplified Chinese) as 
the default encoding.
2. Create a directory containing Chinese characters. Such as C:\测试
3. In the directory create a python file such as C:\测试\test.py
4. In the python file enter the following lines
import traceback
try:
    aaa # create a non-existent name
except Exception as ex:
    traceback.print_exc()
5. Run the program with this command line (remember to use full path to 
the test.py file):
C:\Python31\python.exe C:\测试\test.py
6. See the output.

Expected result:
There is correct output without encoding problems. Such as:

Traceback (most recent call last):
  File "C:\测试\test.py", line 3, in <module>
NameError: name 'aaa' is not defined

Actual result:
UTF-8 encoded string is decoded using CP936 so the output is incorrect.

Traceback (most recent call last):
  File "C:\娴嬭瘯\test.py", line 3, in <module>
NameError: name 'aaa' is not defined

Additional information:
In Python 3.0, such test would generate:
File "<decoding error>", line 221, in main
In Python 3.1, the test generates the output mentioned in the repro 
steps.  As I tried traceback.format_exc(), it seems the original 
characters 测试 have become three Unicode characters when returned by 
format_exc().