BUG: Removed use of cmake 1.4 compatability variable.

Modules/FindFLTK.cmake

@@ -46,7 +46,8 @@ IF(WIN32)
 ENDIF(WIN32)
 
 IF(UNIX)
-  SET( FLTK_PLATFORM_DEPENDENT_LIBS ${CMAKE_X_LIBS}  -lm)
+  INCLUDE(${CMAKE_ROOT}/Modules/FindX11.cmake)
+  SET( FLTK_PLATFORM_DEPENDENT_LIBS ${X11_LIBRARIES} -lm)
 ENDIF(UNIX)
 
 IF(APPLE)