[MacPorts] #56294: boost: update to 1.67.0

[MacPorts]

#56294: boost: update to 1.67.0
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 Reporter:  michaelld  |      Owner:  (none)
     Type:  update     |     Status:  new
 Priority:  Normal     |  Milestone:
Component:  ports      |    Version:
 Keywords:             |       Port:  boost
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 Boost 1.67.0 is out 14-Apr-2018. Updating from current (1.66.0_3) seems to
 work "out of the box", with just rev-bumps to dependent ports -- still
 testing but so far so good for at least my ports. Attaching Portfile diff.

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