Hello Guix,

Here's a proposed patch set that will henceforth enable us to freely
update ImageMagick (and dblatex, and gtk-doc) on our 'master' branch
without grafts.  This is done by adding variables 'imagemagick/stable',
'dblatex/stable', and 'gtk-doc/stable', which are then used as
'native-inputs' in selected packages.

The idea here is that the overwhelming majority of dependencies on
'imagemagick' are via references to 'gtk-doc' in the 'native-inputs' of
GNOME libraries.  The risk of running buggy imagemagick code within Guix
build containers is presumably quite limited, and in any case, grafting
is no better in this regard.

The last 3 commits of this series apply more bug fixes beyond what we
currently have in 'master', including for CVE-2020-27829, as well as a
few other recent upstream commits that look to me potentially security
relevant.

Are there any comments or objections to this approach?

      Mark

Note: I haven't yet fully tested these commits.