Abort FindQt4.cmake if Qt 5 is found.

Modules/FindQt4.cmake

@@ -1169,10 +1169,22 @@ ELSE( Qt4_FIND_COMPONENTS )
 
 ENDIF( Qt4_FIND_COMPONENTS )
 
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(Qt4
-  REQUIRED_VARS ${_QT4_FOUND_REQUIRED_VARS}
-  VERSION_VAR QTVERSION
-  )
+if (${QT_VERSION_MAJOR} GREATER 4)
+    SET(VERSION_MSG "Found unsuitable Qt version \"${QTVERSION}\" from ${QT_QMAKE_EXECUTABLE}")
+    SET(QT4_FOUND FALSE)
+    IF(Qt4_FIND_REQUIRED)
+       MESSAGE( FATAL_ERROR "${VERSION_MSG}, this code requires Qt 4.x")
+    ELSE(Qt4_FIND_REQUIRED)
+      IF(NOT Qt4_FIND_QUIETLY)
+         MESSAGE( STATUS    "${VERSION_MSG}")
+      ENDIF(NOT Qt4_FIND_QUIETLY)
+    ENDIF(Qt4_FIND_REQUIRED)
+else()
+  FIND_PACKAGE_HANDLE_STANDARD_ARGS(Qt4
+    REQUIRED_VARS ${_QT4_FOUND_REQUIRED_VARS}
+    VERSION_VAR QTVERSION
+    )
+endif()
 
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