Make Add and AddAtFront handle multi element paths as strings

[rwmcintosh]

We keep creating new cases of the bug where we try to append a pathelement as a string and it gets added as a single entry, but it actually has the pipe separator in there.

The string overrides for adding elements to a path should handle the cases where the intention is to add a multi-part path rather than a single element. We just have to break it up by the PATH_DELIMITER