The use of built-in CMAKE_CURRENT_LIST_DIR requires at least
CMake 2.8.3. This fix properly defines the variable to allow its
use in versions < 2.8.3 as well.

Fixes issue #4205.

Exclude >= 2.8.3 from reimplementation of CMAKE_CURRENT_LIST_DIR

This avoids violation of possible future CMake policy checks
regarding reserved/read-only variables.