Modified RunnableHandler to process runnables FIFO

Contrary to the expectations of every Handler, I found that the RunnableHandler processes runnables in a LIFO (stack-like fashion).  

The correct approach is to process them in order and then clear the list, as I've done here.  This not only processes the items in FIFO order as expected, it also avoids any overhead of trying to remove the first element of the ArrayList.