Stdstring removal part 0

This is some work by @notspiff at finally removing CStdString from the tree.  It'll come in 3 parts:

1. This part, minor cleanup stuff.
2. A larger part doing prep-work, removing CStdString from common functions and widely derived classes.
3. The largest part doing the main removal.

The biggest question in this one is the UnrarXLib commit.  As far as I'm aware, the proposed change should work, but broad testing would be nice.