1885: First commit of most complete keep proxy, no tests yet.  Removed build.sh
in favor of go.sh that wraps 'go' with the desired GOPATH and 'go get'.  Added
keepclient.Ask() method which does HTTP HEAD.  Added AuthorizedGet() and
AuthorizedAsk() which provide signature and timestamp.
1885: Renamed DiscoverKeepDisks to DiscoverKeepServers, moved error.New()
declarations to the top, changed some tests to use KeepClient copy instead of
pointer.
Merge branch '2798-go-keep-client' into 1885-keep-proxy refs #1885
1885: Stubbed out integration test for proxy
1885: Integration test of proxy work in progress.
Merge remote-tracking branch 'origin/master' into 1885-keep-proxy refs #1885
1885: Full-stack integration test (api+keep+keepproxy+keepclient) works!
1885: GET and HEAD through the proxy work correctly now.  Added invalid API token test.
Merge branch 'master' into 1885-keep-proxy refs #1885
1885: Made ServiceRoots atomically updatable, so that KeepProxy can poll for
changes in the services list without disrupting any active flows.
1885: Fix bug in not returning from the handler on failed authorization.
Improved logging (which uncovered the previous bug.)  Tweaked go.sh and tests.
Merge branch 'master' into 1885-keep-proxy refs #1885
1885: Added logging of invalid requests.  Added logging when the server list is
update.  Improved KeepClient error reporting.
Merge branch '1885-keep-proxy' closes #1885