Fixed an obscure compiler bug involving assignments and indexing, read more

TOY_OP_INDEX_ASSIGN_INTERMEDIATE was being used when it shouldn't have.

Now the check runs down the whole binary->right branch to ensure the given
node doesn't exist in that tree.

test/scripts/index-assignment-intermediate-bugfix.toy

@@ -0,0 +1,10 @@
+
+var result; //result must exist to ensure assingment, rather than declaration is invoked by the comparison below
+
+var lhs = [0];
+var rhs = [0];
+
+result = lhs[0] < rhs[0]; //make sure this doesn't invoke TOY_OP_INDEX_ASSIGN_INTERMEDIATE
+
+
+print "All good";