Simon Willnauer 574d1b35b3 Replace ContextAndHeaders with a ThreadPool based ThreadLocal implementation
ContextAndHeaders has a massive impact on the core infrastructure since it has to
be manually passed on to all relevant places across threads/network calls etc. For the same reason
it's also very error prone and easily forgotten on potentially relevant APIs.

The new ThreadContext is associated with a ThreadPool (node or transport client) and ensures that
headers and context registered on a current thread are inherited to new threads spawned, send across
the network to be deserialized on the receiver end as well as restored on the response handling thread
once the response is received.
2016-01-13 11:53:32 +01:00
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