[MacPorts] #50671: boost: Update to 1.60.0

[MacPorts]

#50671: boost: Update to 1.60.0
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  Reporter:  eborisch@…  |      Owner:  ryandesign@…
      Type:  update      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.3.4
Resolution:              |   Keywords:  haspatch
      Port:  boost       |
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Comment (by ryandesign@…):

 A developer must manually identify all ports that use boost, manually
 increase their revisions, verify they all build and if necessary fix any
 bugs, and commit everything together. This involved process is why I
 haven't done it.

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Ticket URL: <https://trac.macports.org/ticket/50671#comment:8>
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