This commit

+ provides a template type to `make_shared` so that
  clang (Xcode 7.3.1, Mac OS X 10.11 SDK) and other compilers
  will use native shared pointers instead of Boost's implementation.
+ adds shiboken guards around the Boost `shared_ptr` includes
  used as a fallback when no system shared pointers are detected.
+ adds shiboken guards around Boost `function` headers if they are
  used to provide C++11 function, bind, and placeholder features.