[MacPorts] #56294: boost: update to 1.68.0 (was: boost: update to 1.67.0)

[MacPorts]

#56294: boost: update to 1.68.0
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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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Description changed by michaelld:

Old description:

> 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.

New description:

 Boost 1.68.0 is out 09-Aug-2018, and builds with no significant changes to
 the port patches or Portfile. 1.67.0 built with no significant changes to
 the port patches or Portfile, but many dependent ports had a compatibility
 issues with 1.67.0; hopefully the vast majority of those have been
 resolved, given that it was out 14-Apr-2018 -- about 4 months ago.

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Ticket URL: <https://trac.macports.org/ticket/56294#comment:4>
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