Installing supervisor on Natty Nat will undoubtedly throw the error
ImportError: cannot import name fixtag
The root cause of this error is the
python-meld3 library and the following import statement:
from xml.etree.ElementTree import fixtag
The problem has been fixed in version 0.6.7 of python-meld3. Therefore, before you install supervisor, do the following on the command line as root:
aptitude install python-meld3 pip install meld3==0.6.7
The above will install version 0.6.5 of python-meld3 and then pip will upgrade it to the latest. You can then install supervisor without any problems.
If you want you can read the gory details of the problem in python-meld3.