boost::shared_ptr -> std::shared_ptr

Makefile

src/boost/checked_delete.hpp

src/boost/detail/shared_count.hpp

src/boost/detail/workaround.hpp

src/boost/enable_shared_from_this.hpp

src/boost/shared_ptr.hpp

src/boost/weak_ptr.hpp

src/libexpr/eval.cc

src/libstore/build.cc

src/libstore/gc.cc

src/libstore/store-api.cc

src/libstore/store-api.hh

src/nix-daemon/nix-daemon.cc