dvdauthor: update to 0.7.2

Depends on ImageMagic6 due to use of deprecated interface.

0.7.2: 2016 December 31
Various code-quality and build improvements
Support "jump pgc n" and other interaction code-generation improvements
Improve reliability of dvdunauthor
Don't force infinite pause on last cell of a PGC
Allow specification of provider field in VMG IFO file
Add video_format(7) man page
Add padding to ensure .BUP and .IFO files end up in different ECC blocks
Enabled hinting of rendered subtitle text
Require cell start and end times (if specified) to be nonempty

(rhialto)