wxSmith ExtraCode Patch

[ZinnJonas]

Hey all,

currently i was using the ExtraCode feature of wxSmith more often.
But I was not able to find a self-reference in it.

So if you chance the variable name later you have to change the name in the ExtraCode block to.

So i added a small patch, which allow the usage of $(THIS) in an ExtraCode block. This will be
replaced with this or the current VarName.

It may help someone.

best regards,
zinnjonas