Don't delete anything from the temporary directory if unsure

Don't delete anything from the temporary directory if unsure

Sarg must delete any previous stray temporary directory before filling it
with the current log data. But sarg must not just delete any directory and
its content if it isn't ours. Therefore, sarg check the directory content
to make sure that it only contains files that may belong to us.

There was an error in that routine. It would recursively delete directories
found in the candidate temporary directory before making sure the whole
directory content can be safely deleted.

This problem is fixed here.