dirent_uri assertion in trunk

[Daniel Shahaf]

% $svn log 
https://svn.apache.org/repos/infra/websites/production/www/content@PREV
subversion/libsvn_subr/dirent_uri.c:1571: (apr_err=235000)
svn: E235000: In file 'subversion/libsvn_subr/dirent_uri.c' line 1571: 
assertion failed (! svn_path_is_url(relative))