Update graphics/ImageMagick to 7.0.2.4

pkgsrc changes:
- Add a comment to suggest running upload-distfiles because upstream only store
  latest stable version distfiles.

Changes:
7.0.2-4:
  * To comply with the SVG standard, use stroke-opacity for transparent strokes.
  * Define CompositeChannels mask to Red, Green, Blue, Alpha, and Black.

7.0.2-3:
  * Patch so -kuwahara option can preserve colormapped edges.
  * The histogram coder now returns the correct extent.
  * Use CopyMagickString() rather than CopyMagickMemory() for strings.

(leot)