In RHEL4, the following entries in Config::CONFIG in rbconfig depended on DESTDIR; in the latest rawhide ruby they don't anymore. That makes it almost impossible to use certain install.rb scripts from a specfile. The entries that should once again depend on DESTDIR are sitelibdir and sitearchdir (and with that probably _fc_sitedir) This bug also affects older versions of FC, especially FC5. A fix to this should also fix all active FC branches, so that specfiles can run install.rb across all active branches
should be fixed in 1.8.5-2.fc6.