There were some areas where we weren't doing a great job of handling

caching or generating ETags. We also had a bug in a recent change that

prevented us from having reliable ETags.
The recent addition of TEMPLATE_SERIAL didn't end up creating a stable

serial. The assumption the code made was that a call to

generate_ajax_serial() would always re-calculate the proper value based

on the modified time of the templates, but this actually only happens

the first time. That meant that every time initialize() was called, we'd

change TEMPLATE_SERIAL, making it unstable. We're a bit more careful

now to only set this once.
We had some less-than-optimal ETags, which basically just exposed some

state, generating longer and longer ETags as we added to them. We now

compute a hash based on these values.
We also had a couple cache checks based on the Last-Modified timestamp,

but this isn't a great thing to base caching off of. They're not

flexible, and they come with precision issues and can end up being

ignored based on other headers. We now use ETags instead.

Unit tests pass.
Verified that I got repeated 304s on these views, so long as the source of

the ETags did not change.
This also fixed the odd little bug with the Review Request Last Update URL,

where every other request would return a 200 instead of a 304.