DS-1754 Use canonical not absolute path

Using the canonical path when determining the location of the undo information
leads to consistent behaviour when using "." as the source vs using eg an
absolute path. This also adds the name of the directory to the error message in
case the directory cannot be created, to help with troubleshooting.
Merge pull request #375 from aschweer/DS-1754

DS-1754 Use canonical not absolute path