path precedence -- clean up old versions of tools from $PATH

[kristovatlas]

In order to make sure that the latest version of programs are run, this tool sometimes edits the $PATH variable, explicitly placing the latest version at the front. In doing so, it often leaves the old version of the tool in $PATH further down. This doesn't have any known negative effect except that it junks up $PATH in an impolite way.

Solution: Modify config check fix command to first remove all versions of the tool from $PATH and then add the latest to the front.