Remove unnecessary language initializations. Change the main
CMakeLists.txt project() call to specify NONE. Use enable_language(CXX)
instead of project() in cases that need it to avoid enabling C too.
Commit b8259c3d (Centralize maintenance of usage requirement include
directories, 2013-04-29) changed the handling of the property.
Previously setting the property directly instead of via
target_link_libraries would not result in transitive include
directory handling.
This is a partial revert of commit 77cecb77 (Add includes and compile
definitions with target_link_libraries., 2012-11-05).
As the interface includes and defines are now determined by the link
closure, there is no need to populate the corresponding properties
explicitly.
Brad King
Stephen Kelly