Run memcached tests on Travis

* Only build libmemcached and the executable for deploys.
* `code.google.com/p/go.net` has [moved to](https://golang.org/s/go14subrepo) `golang.org/x/net`.
* Update envconf to pick up fixes for decoding pointers and unexported fields.
* Update go-etcd to pick up [locking](https://github.com/coreos/go-etcd/commit/031b60a0eec69d8d188df7cb23eb346eadd46e02) and [response parsing](https://github.com/coreos/go-etcd/commit/755c7f2f4a682b6a9ac6482483236db55d0c6f6d) fixes.