Fixes issue #661 - debug trace not sampled

[tgeens]

The test SamplingFlagsTest#debugImpliesSampled uses a Builder to construct a SamplingFlags object. The problem is that the Builder contains the logic that implicitly enables sampling, when the debug flag is set. But not all sampling-flags are created using that Builder!

The solution provided here is moving the logic back to the .sampled() method, for both:

1. SamplingFlagsImpl.sampled() and
2. the static Boolean sampled(int flags) used by TraceContext and TraceIdContext

This should resolve issue #661

[codefromthecrypt]

sorry I didn't see this. I appreciate your help, but since I've made #663 with tests and such are you ok with me closing this?

[codefromthecrypt]

otherwise you can merge my changes into yours.. your choice

[codefromthecrypt]

thank you for this change. I fixed it in a different way in #663 which allows me to immediately release a patch for you. Please do help again next time!