I think the general policy should be to always log errno using both
Util::symbolicErrno() and std::strerror(), never log a naked errno.
But only in cases where we know that it is highly likely that it is
the most recent system call that has failed, so errno makes sense.
Change-Id: I4a1fb31e375ea949e7da17687464361efe7c1761
Dung out overlapping return enumerations. Move more work into 'move'
callbacks at a safer time, etc.
Change-Id: I62ba5a35f12073b7b9c8de4674be9dae519a8aca
