resourceloader: Set a TTL for minification cache entries
Follows-up 458e7cabbbafd. HHVM's APC cache doesn't have any
limitation or eviction logic. Thus entries without a TTL will
At time of writing over 99% of APC entries were from "resourceloader:filter"
because there are far more unpopular resources than popular ones.
A fixed TTL is suboptimal as it will also cause popular resources
(e.g. startup module, or jquery) to be re-minified every day.
Beware this isn't one single minification. It's one minification,
for every JS/CSS resource, on every app server, for many different