Create special replacement even for <<-

Now when the reading and writing of the target is responsibility of
ReplacementNode, SpecialReplacementNode works even with <<- (super)

com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/control/ReplacementNode.java

@@ -109,7 +109,7 @@ abstract class ReplacementNode extends RNode {
     private ReplacementBase createReplacementNode(boolean useSpecials) {
         CompilerAsserts.neverPartOfCompilation();
         // Note: if specials are turned off in FastR, onlySpecials will never be true
-        boolean createSpecial = hasOnlySpecialCalls() && useSpecials && !isSuper;
+        boolean createSpecial = hasOnlySpecialCalls() && useSpecials;
         return createSpecial ? createSpecialReplacement(source, calls) : createGenericReplacement(source, calls);
     }