Do not print exception message below stacktrace

because it prints Unicode characters escaped, and we have already formatted the message above. 

also a typo fix.

please review: @sarina, @polesye, @auraz, @olmar 
Indentation doesn't meet style guidelines (https://github.com/edx/edx-platform/wiki/Python-Guidelines)
```python
tb=cgi.escape(
    u''.join(['Traceback (most recent call last):\n'] +
    traceback.format_tb(sys.exc_info()[2])))
)
```