make setup error a little more verbose

if a subdir is not setup properly, then init_paths() in inc/init.php will use
the pretty name ("datadir" instead of "pages"; "olddir" instead of "attic").
attached patch simply includes the actual directory name in the output so
people dont have to look it up in the source
code.

darcs-hash:20061211194244-5224c-2d22eeb08d770108d1d993783e95d11bef0e8855.gz