Revert "Eliminated magic from the to_unitless method in UnitAssigner. Objects created by to_unitless should now be pickle-able (needs a test)"

This reverts commit 0cbc6fd6f037f1894cbfeec124f807e4835b9ef4.
Revert "Revert "Eliminated magic from the to_unitless method in UnitAssigner. Objects created by to_unitless should now be pickle-able (needs a test)""

This reverts commit dcdaf89b54285a2aca93b8e5cd338eb0467b7b50.
Revert "Try testing python 2.6 as well as python 2.7"

This reverts commit 02f0329a4722aba9951ee7b3b1d7d2c67740ae07.