Comment out accidentally left over 'raise'.

This function promises NEVER to raise an exception, I was propagating it out
while debugging some odd behavior with __builtins__ and left it accidentally
in place.

IPython/core/prompts.py

@@ -221,7 +221,7 b' def str_safe(arg):'
             out = '<ERROR: %s>' % msg
     except Exception,msg:
         out = '<ERROR: %s>' % msg
-        raise  # dbg
+        #raise  # dbg
     return out
 
 class BasePrompt(object):