ImageMagick ports: Default to version 7; replace slaves with flavors

[jrm]

Summary

I am still testing all the ports dependencies. I will update soon.

PR:
Submitted by:
Reported by:

[jrm]

Re-add PORTEPOC=1 to graphics/ImageMagick

[jrm]

After testing all ports depending on ImageMagick, set some ports to depend on graphics/ImageMagick6.

[kwm]

Sorry for the long wait on replying. I was in the impression I already submitted this..

So console command syntax and API where changed in ImageMagick 7. So this is/can be a very serious issue for users. If a user uses IM6 as a "stand-alone" port, building other ports will not show this use case.

https://abi-laboratory.pro/index.php?view=timeline&l=imagemagick

Instead of doing a version dance, I would like to promote adamw@'s suggestion of renaming graphics/ImageMagick to graphics/ImageMagick6 (and adding pkgnamesuffix=6). And don't switch the ports. This way we there isn't a "main" ImageMagick port, but two versions instead.

While the 6 series is marked "legacy", upstream isn't planning of stopping fixing bugs in the 6.x series any time soon. As in a good number of years.

[jrm]

Sounds good.