bug#29584: imagemagick-types-inhibit does not result in correct image backend (minor)

[Adam Plaice <plaiceadam@gmail.com>]

Thanks for the clarification.

As it's a deliberate change and to avoid over-complication that nobody
usually needs (if one generally dislikes the imagemagick backend then
one should use a version of emacs compiled without it, and in the very
rare case when one does need to change the backend on the fly, one can
just override image-toggle-display-image), leaving the code alone is
probably the best option.

However, I'd argue that the documentation should be updated — the
docstring of imagemagick-types-inhibit already contains extensive
warnings

"
If you change this without using customize, you must call
‘imagemagick-register-types’ afterwards.

If Emacs is compiled without ImageMagick support, this variable
has no effect.
"

so another sentence to the effect of "If emacs is compiled with
alternative image backends, in addition to ImageMagick support, this
variable also has no effect." wouldn't be out place (and since there
are already extensive warnings, creating an impression of
completeness, the absence of an important warning — having multiple sets
of backends is probably the most frequent situation on GNU/Linux —
would be confusing).