clock: test program modified to use common data

Generates test data from JSON in x-common.  This brings some minor changes to the test cases as a result of looking through other languages and collecting a common core of test cases.  I don't expect it to break existing Go solutions though except for the addition of TestVersion.

The new file `cases_test.go` should get fetched by the client.  The new file `example_gen.go` should not get fetched.