Pipelet

I think we should catch this and print something less dramatic like:
no computed pipeline
Here is the full exception and traceback:

500 Internal Server Error

The server encountered an unexpected condition which prevented it from fulfilling the request.

Traceback (most recent call last):
File "/usr/lib/pymodules/python2.6/cherrypy/_cprequest.py", line 606, in respond
cherrypy.response.body = self.handler()
File "/usr/lib/pymodules/python2.6/cherrypy/_cpdispatch.py", line 25, in call
return self.callable(*self.args, **self.kwargs)
File "/usr/local/lib/python2.6/dist-packages/pipelet/web.py", line 287, in index
log_dir = l⁰[1].split("_")[0]
IndexError: list index out of range