ref #1657 [Thread optimization]

http://redmine.named-data.net/issues/1657
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- decreased CPU loading in idle mode (when no producer exists with the
name being fetched)
[untracked] updated Makefile for dependencies on header files
ref #1657 [Thread optimization]

http://redmine.named-data.net/projects/ndnrtc/issues
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- fixed CPU overload on rebufferings
'issues/1657-thread-optimization' -> 'dev'