Leaking cancel contexts.

The client uses WithContext to create a context for signaling shutdown to sub go-routines. This seems to make the context leak when the workers return without cancelling the context. The cancel function must be run always.

It seams the context that is generated on 'Start' is leaked at least if the Dial fails. The workaround is to call Stop always. There or other contexts that are generated via WithCancel, that look suspiciously like leaks, but I didn't check if that is the case.