COMP: We now require CMake 2.4.5 or higher to build

We use the CMakeDependentOption module unconditionally, so we must
require a version of CMake new enough to provide it.

CMakeLists.txt

+CMAKE_MINIMUM_REQUIRED(VERSION 2.4.5 FATAL_ERROR)
 PROJECT(CMake)
-CMAKE_MINIMUM_REQUIRED(VERSION 2.4 FATAL_ERROR) 
 IF(COMMAND CMAKE_POLICY)
   CMAKE_POLICY(SET CMP0003 NEW)
 ENDIF(COMMAND CMAKE_POLICY)