[MacPorts] #51310: ImageMagick: update to 7.x

[MacPorts]

#51310: ImageMagick: update to 7.x
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  Reporter:  mopihopi     |      Owner:  ryandesign
      Type:  update       |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  ImageMagick  |
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Comment (by kencu):

 I am not seeing in your branch how you handled having the two different
 versions installed at the same time, or how a port that wants to use one
 or the other, via say pkgconfig, can specify that reliably.

 Perhaps I am missing the "magic" ;)

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Ticket URL: <https://trac.macports.org/ticket/51310#comment:32>
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