ENH: fix for backwards compatibility

Modules/FindDoxygen.cmake

@@ -26,9 +26,9 @@ SET(CMAKE_FIND_APPBUNDLE "NEVER")
 # For backwards compatibility support
 # DOXYGEN_FIND_QUIETLY, but it should have been
 # Doxygen_FIND_QUIETLY.  
-IF(DOXYGEN_FIND_QUIETLY)
-  SET(Doxygen_FIND_QUIETLY)
-ENDIF(DOXYGEN_FIND_QUIETLY)
+IF(Doxygen_FIND_QUIETLY)
+  SET(DOXYGEN_FIND_QUIETLY TRUE)
+ENDIF(Doxygen_FIND_QUIETLY)
 
 IF (NOT DOXYGEN_FIND_QUIETLY)
   MESSAGE(STATUS "Looking for doxygen...")