[MacPorts] #61050: Add `port vercmp` command

[MacPorts]

#61050: Add `port vercmp` command
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  Reporter:  ryandesign   |      Owner:  (none)
      Type:  enhancement  |     Status:  new
  Priority:  Normal       |  Milestone:
 Component:  base         |    Version:  2.6.99
Resolution:               |   Keywords:
      Port:               |
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Comment (by ryandesign):

 Or if it is too difficult or weird for the `port` command to process its
 arguments in a way that is not names of ports, then we could ship a `port-
 vercmp` script.

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Ticket URL: <https://trac.macports.org/ticket/61050#comment:1>
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