Blacklist Qt 4.5.0 as promised

I know this is annoying, but it is too difficult to maintain.
If you are a maintainer, you can revert this commit, but this isn't advised

modules/gui/qt4/qt4.hpp

@@ -36,10 +36,10 @@
 #include <QString>
 
 #if ( QT_VERSION < 0x040400 )
-# error Update your Qt version
+# error Update your Qt version to at least 4.4.0
 #endif
 #if QT_VERSION == 0x040500
-# warning Please update Qt version to 4.5.1. This warning will become an error.
+# error Please update Qt version to 4.5.1. 4.5.0 is too buggy
 #endif
 
 enum {