The CMake module FindBoost.cmake searchs for Boost first in the "Config
mode" of 'find_package'. That allows to find installation of boost-cmake
(that is Boost configured using CMake). That configuration of Boost is
rather rare. But the search for it leaves a variable Boost_DIR=NOTFOUND in
the cache, even if Boost libraries are found using the regular way.
That patch removes from the cache the variable Boost_DIR, when Boost is
already found, to avoid more confusion for users.
As of Boost 1.50 it is required to link Boost.System with CGAL. System
has been a Thread dependency all along and we simply never linked to
it and apparently got lucky.
Add it to the dependencies, add it in the manual and INSTALL file.
CGAL_Boost_USE_STATIC_LIBS is now an (advanced) CMake option on all
platforms, and is stored in the generated CGALConfig.cmake. That way, its
value is proposed as the default value for the same option when programs
using CGAL are configured using CMake.
The script UseCGAL includes the module CGAL_TweakFindBoost, to define
Boost_USE_STATIC_LIBS and Boost_ADDITIONAL_VERSIONS.