stdlib: Fix StringValue + and * operators
stdlib: Fix StringValue + and * operators

They act more like you'd expect now.  Some of the other Value types
have similar issues, but this commit doesn't fix them...

AbePralle/Rogue,Plasmaworks/Rogue,Plasmaworks/Rogue,Plasmaworks/Rogue,AbePralle/Rogue,Plasmaworks/Rogue