[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 ryandesign):

 If we choose your method of having separate ports, then adding `port
 select` is great for user convenience, but it is inapplicable to
 individual ports that depend on a version of ImageMagick and can also be
 problematic for them.

 I still want to know if we must separate the ports in the way that you
 suggest or if there is a less invasive solution. ImageMagick 6 and 7 have
 different program names, so they don't conflict and could remain in the
 standard bin directory where other ports and programs would not need to be
 told where to look for them. Remaining questions were whether the same
 applies to all the other files the two versions install.

 I've gone over this before in comment:19.

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Ticket URL: <https://trac.macports.org/ticket/51310#comment:36>
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