structured diff between pairs of executions to reveal first divergence

[bestchai]

The current diff-ing of two executions performs matching of events regardless of their sequence. It would be helpful to complement this functionality with a diff that compares the sequence of events (as well as ordering relationships between events) from top to bottom and stops and highlights the first deviation. That is, if in one execution the local host events are a,b,c and in another the local host events are a,b,b then the second 'b' event in the second execution would be highlighted. Likewise, the events that have different -partial- ordering would also be highlighted (e.g., if the first 'b' in the second execution also came before another event at a different host, then it would be highlighted as the first deviation, instead of the second 'b' event in the second execution).

[Issue created by bestchai: 2015-08-28]