std::unique_ptr

This work is still in progress / more patches to come in the series. I'd like to get a basic Ack that this is a reasonable direction to go in.

Overall the goal is to get rid of / reduce the number of instances of new + delete in our codebase, in line with C++11 best practices of eliminating unnecessary raw pointers. My general approach is that whoever has the delete gets ownership. If it's the only thing which ever owns it, I promote to a member instead of dealing with pointers at all.

@JasonL9000, @jmlvanre: Is the patch for making arena a member of TCoreVector reasonable to you? (There are more cases where the same code pattern appears and I'd like to convert the others in the same manner. Eliminate all hand memory management, rather than even going through unique_ptr)