CMakeLists.txt tweaks for OS x and Clang. list(append...) will not always work for CMAKE_CXX_FLAGS for reasons I don't know. Clang also requires the use of -stdlib=libc++.
CMakeLists.txt comments
For some reason Clang does not support std::ostream operator bool. Workaround.
Use libc++ only on apple machines.
Merge branch 'cmake' into lb-refactor