[MacPorts] #56294: boost: update to 1.67.0

[MacPorts]

#56294: boost: update to 1.67.0
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  Reporter:  michaelld  |      Owner:  ryandesign
      Type:  update     |     Status:  assigned
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:
Resolution:             |   Keywords:
      Port:  boost      |
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Comment (by michaelld):

 OK so there are some issues I'm coming upon with changes to
 `boost::thread` and `boost::posix_time` ... hopefully it's just slopping
 programming on the project's part. Or maybe the Boost folks fixed some
 type conversation issues. I'll work on fixing & verify back backward
 compatibility with (at least) boost 1.66.0.

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Ticket URL: <https://trac.macports.org/ticket/56294#comment:2>
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