Fixes bug #2147 http://moodle.org/bugs/bug.php?op=show&bugid=2147
The config.php generated by install.php was missing $CFG->admin -- credit goes to serge.laot@wanadoo.fr for the report and patch.
$str .= '$CFG->wwwroot = \''.$INSTALL['wwwroot']."';\r\n";
$str .= '$CFG->dirroot = \''.$INSTALL['dirroot']."';\r\n";
$str .= '$CFG->dataroot = \''.$INSTALL['dataroot']."';\r\n";
+ $str .= '$CFG->admin = \''.$INSTALL['admindirname']."';\r\n";
$str .= "\r\n";
$str .= '$CFG->directorypermissions = 0777;'."\r\n";