feature request: option for specifying frequency of snapshots during test execution

[mmaypumphrey]

We're finding the snapshots taken during execution more and more useful. For example, a bug I filed yesterday involved an extraneous horizontal white line in the middle of a blue pop-up. I detected it by absent-mindedly glancing at my test machine during a run. However, that image wasn't captured by pysaunter because it happened in the middle of one of the intervals between captures. If we could specify a smaller interval via the cmdline (or conf.ini), that would allow us to capture more of the action. (And no--I'm not asking for video here!)

Another example: I recently discovered when setting up a new test account that an upgrade page included some extraneous text. This kind of problem is virtually impossible to discover in a straightforward automated way. But we could have caught this one by quickly flicking through all the images captured during the pysaunter execution run, as we have a test that lands on this page.