[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 FranklinYu):

 I think it's easier to build a separate ImageMagick7 and then update those
 61 ports when necessary. Some of these ports may not even be maintained so
 bumping them should be a lower priority than providing a latest
 ImageMagick.

 By the way, as a new MacPorts user I was wondering whether there is any
 way to smoothly migrate ImageMagick to ImageMagick6? It’s not strictly
 required but good to have this rename.

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Ticket URL: <https://trac.macports.org/ticket/51310#comment:16>
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