Write Qt version into pkg config file.

CMakeLists.txt

@@ -52,12 +52,14 @@ MESSAGE(STATUS "Looking for Qt ${DESIRED_QT_VERSION_MAJOR}.")
 SET(CMAKE_INCLUDE_CURRENT_DIR ON)
 IF(USE_QT4)
   FIND_PACKAGE(Qt4 REQUIRED QtCore QtGui QtOpenGl QtNetwork)
+  SET(PKG_CONFIG_EXTRA "qtversion: ${QT_VERSION_MAJOR}.${QT_VERSION_MINOR}.${QT_VERSION_PATCH}")
 ELSE(USE_QT4)
   FOREACH (component "Core" "Widgets" "Gui" "OpenGL" "Concurrent" "Network")
     FIND_PACKAGE ("Qt5${component}" REQUIRED)
     LIST(APPEND QT_INCLUDE_DIRS ${Qt5${component}_INCLUDE_DIRS})
     LIST(APPEND QT_LIBRARIES    ${Qt5${component}_LIBRARIES}   )
   ENDFOREACH (component "Core" "Widgets" "Gui" "OpenGL" "Network")
+  SET(PKG_CONFIG_EXTRA "qtversion=${Qt5Core_VERSION}")
 ENDIF(USE_QT4)
 
 SET(BOOST_COMPONENTS thread regex)