Queue of std::shared_ptr to queue of std::unique_ptr?

[gvansickle]

Globber/DirTree use a "sync_queue<std::shared_ptr>& m_out_queue;" to move FileIDs from the globbing threads to the scanning threads. It's not clear to me atm why these couldn't be "sync_queue<std::unique_ptr...", though there might be a reason I'm not thinking of. Changing to unique_ptr, if possible, would eliminate ref counting overhead.