Prints show in reverse order of merge of statement blocks

As pointed out by dusenberrymw - prints currently show up in reverse order after the merge of sequences of statement blocks. For instance, the following example

print("test1");
print("test"+2);
print("test"+3);
if(1==1){} 
print("test4");
print("test"+5);

currently produces the following output

test4
test5
test1
test2
test3

The new instruction scheduling introduced with SYSTEMML-2039 ensures (as a byproduct) that prints within one DAG are scheduled in their original order. However, after the merge of statement blocks, prints without data dependencies can be reordered.

This task aims to simply sort all DAG output instructions accordingly to their line numbers. Note that his only affects the new instruction scheduling as used for spark, hybrid_spark, and singlenode.