Remove usage of CMAKE_CURRENT_LIST_DIR now that we have CMP0017

This puts the new search behaviour for included files in action, i.e.
now when a file from Modules/ include()s another file, it also gets the
one from Modules/ included, i.e. the one it expects.

Alex

Modules/FindThreads.cmake

@@ -153,5 +153,5 @@ IF(CMAKE_USE_PTHREADS_INIT)
   ENDIF()
 ENDIF(CMAKE_USE_PTHREADS_INIT)
 
-INCLUDE("${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake")
+INCLUDE(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(Threads DEFAULT_MSG Threads_FOUND)