app/cache: store memcache values as gzipped gobs
app/cache: store memcache values as gzipped gobs

We're running up against the 1MB value limit when serving the dashboard
front page. Rather than shard keys, just store a more compact
representation of the data.

Change-Id: Ib5a4db4b0b78ddfe711ecbb58dcf1eff18e1fd53
Reviewed-on: https://go-review.googlesource.com/14630
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

proppy/build,golang/build,proppy/build,proppy/build,golang/build,golang/build,proppy/build,golang/build