SPDY/HTTP2 requests are stacking on top of each other

[ewinslow]

Note the green bars (waiting for server response) in the request below, when at the lowest throttle level (50Kbps, 500ms RTT):

The problem is even more pronounced over a fast connection because blue bars (download times) are reduced substantially.

It seems like there's about 40-80ms of overhead per request, and these get stacked up on top of each other with a lot of requests.

My initial suspicion is that it is just the overhead of running PHP to fetch raw files, and if we actually set up that symlink to the dataroot feature, we'll see a substantial reduction in this aspect of latency... so yay!