Add faster implementation for SmileFunction_CreateExternal.
Add faster implementation for SmileFunction_CreateExternal.

- Note that this has a consequence, in that the name of external functions cannot be more than 256 characters.  It's highly unlikely anyone will hit this in practice, but if you do, there you go.

seanofw/smile,seanofw/smile,seanofw/smile,seanofw/smile,seanofw/smile,seanofw/smile