Investigate divergent merges in concolic mode.

[BenSpencer]

In certain examples from the concolic sites testing we have seen some divergent merges. This is when the newly recorded trace does not match the expected path in the execution tree.

The examples which show these: flyfrontier (1), jetblue (3), monarch (3), united (2)

Unless this is caused by a bug, it means that we are seeing different JavaScript being executed on different iterations. Is this really happening and why?