Fix error reporting in LValue.luaBinOpUnknown.

Since this method always fails with an error message, it should report its
own type, rather than the type of the other object, in the message.

src/core/org/luaj/vm/LValue.java

@@ -68,7 +68,7 @@ public class LValue {
 
 	// unsupported except for numbers
 	public LValue luaBinOpUnknown(int opcode, LValue lhs) {
-		return arithmeticError(lhs.luaGetTypeName());
+		return arithmeticError(luaGetTypeName());
 	}
 
 	// unsupported except for numbers