moved repo to mesos/mesos-go.
Added atomic operation to avoid data race.

Note: slave's health check is still not conflict serializable with
registered, reregistered and connected.
Added tests to test executor driver starting.
Updated mock's reversion.
Fixed mocked test.
Added tests for executor driver's registered().
Added mocked_messenger for testing executor.

Finished testing executor.Start().
Removed mocked slave.
Added license.
Put slave health checker in package healthchecker.

Also put mocked messenger in package messenger.
Also added a mocked health checker for testing.
Added healch check test.
Changed to httptest to benchmark messenger.
Changed slave's upid to be the random generated one.
Splitted http_transporter from transporter.go
Added Driver stop test. Fixed a bunch of things.
removed binary example_executor, added to .gitignore.
changed messenger to allow multiple start() stop().

Also added more tests on the executor.
Merge pull request #18 from vladimirvivien/pure

removed binary example_executor, added to .gitignore.
Remove unsafe and atomic stuffs. Replaced by mutex lock.
Merge branch 'pure' of github.com:mesos/mesos-go into pure