Clarify 304 responses in HUD (and/or client)

[philliphoff]

When the server returns a 304 response, the browser page and HUD are refreshed. However, the HUD then reflects a combination of the original (non-304) request as well as the new one. For example, the timing reflects the 304 request but the button to open the Glimpse client links to the original request.

This can be confusing as:

• The timing data will be different between the HUD and the linked-to request in the client
• The HUD also seems to not show the correct number of fetch/XHR requests (as shown in the screenshot).

Refreshing the page always shows (only) the first 2 AJAX requests:

Making a new AJAX request increments the number:

Opening the Glimpse client shows many more AJAX requests: