[MacPorts] #58097: carthage @0.31.2: add shell completions

[MacPorts]

#58097: carthage @0.31.2: add shell completions
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  Reporter:  FranklinYu   |      Owner:  saagarjha
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  carthage     |
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Comment (by saagarjha):

 Yeah, I always run beta versions. I've already made the changes locally,
 so I can push them if you want to look at them.

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Ticket URL: <https://trac.macports.org/ticket/58097#comment:6>
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