Use std::unique_ptr to replace "scoped" classes like ats_scope_fd and the MutexLock classes

[shinrich]

Now that we have committed to c++11, we can replace our own scoped logic with std::unique_ptr.

[SolidWallOfCode]

This can be done by overriding / supplying a deleter for std::unique_ptr. I think we will probably want to keep our classes for this but change the underlying implementation to be based on std::unique_ptr with just a shim to set the deleter appropriately.

[nekomachi-touge]

I’m considering working on this.
I noticed ats_scoped_str is almost like std::string.
What is the intention for this class?