Issue 3148 xhr polling

@jrgm and @kparlante - could you review this?

There are two commits, the first is a test for the change that @ozten did a little while ago to strip GET data from the submitted URL.

The second is to consolidate consecutive XHR requests to the same URL into one entry.

@kparlante - when the event starts with xhr_complete, there may be a 4th item in the event's array - the number of consecutive times the xhr event was called. If the URL was only called once, the count is omitted.

fixes #3148