Check ephemeral data caching works as expected

[cammoore]

Reported by rbrewer, Aug 12, 2012
The ephemeral data caching does not seem to work as expected in all cases. For example, the source summary does not seem to take into account cached data, and direct SensorData retrieval via REST API didn't work in earlier tests. This calls for a comprehensive survey of all REST and Visualization API methods to make sure they are using the cache when they should be.

Also, we need a ephemeral data caching wiki page that explains how to enable it and what it does.