To avoid treating a repository url as an SVNParentPath url, add some more checks:
* if we already have log entries for the url, just accept the error and skip the SVNParentPath check
* only check for SVNParentPath if the error is either SVN_ERR_RA_DAV_RELOCATED or SVN_ERR_RA_DAV_REQUEST_FAILED - other errors indicate not a permanent problem and therefore indicate that the url still could be a repository url.
