Fix problem if temp dir is on different partition

After downloading a book we try to move the downloaded book if it is
on the same volume as the destination directory. The detection if it's
the same directory needs to be done differently on Linux. This change
partially fixes BL-497.
Refactor reporting of problem when downloading book

When we download a book we don't start the full application. This means
that there might not be a ShellWindow available. This change tries to
invoke the error reporting dialog on the shell window if it is available
and otherwise directly call the Palaso reporting method.
Merge pull request #92 from ermshiperete/BL-497

Fix downloading from BloomLibrary on Linux (BL-497)