The previous implementation failed to prevent duplicates if the entry
being added was the only entry already present in the path. The reason
is that it always required a : to be present in order to remove the new
entry before adding it.
The new implementation is clearer and solves that. However, if the new
entry is already present it will be kept where it was, not moved to the
front of the list. This is fine at the moment.
Fernando Schauenburg
6c7b29705e