Make QT an actual requirement

CMakeLists.txt

@@ -132,7 +132,7 @@ endif()
 
 NICE_OPTION(WITH_QT "Build with Qt" ON)
 if(WITH_QT)
-  FIND_PACKAGE(Qt4)# COMPONENTS Qt3Support QtOpenGl)
+  FIND_PACKAGE(Qt4 REQUIRED)# COMPONENTS Qt3Support QtOpenGl)
   SET(QT_USE_QTOPENGL TRUE)
   SET(QT_USE_QTXML TRUE)
   SET(QT_USE_QT3SUPPORT TRUE)