amoffat/sh — pull request #207 by themalkolm (2014-11-30 00:20:54+00:00)
Title: Include original path in CommandNotFound.

Whenever `which()` fails to resolve the path it returns `None` and
overwrites the original `path` value. Later when we create
`CommandNotFound` exception we always pass `None` instead of the
original `path` value and it makes `CommandNotFound` not so usefull.