installation wizard error in my windows local wamp installation

The issue #255 is addressed here:
 1. error page now works with no configuration.inc.php file at all
 2. QApplicationBase works with no configuration.inc.php file at all
 2. The `__SUBDIRECTORY__` constant formed by installer is always created with leading '/' character
Merge pull request #277 from olegabr/bug-255

installation wizard error in my windows local wamp installation