bug#19889: bug#22207: emacs-25 mishandles info code text on Fedora 23

[Paul Eggert <eggert@cs.ucla.edu>]

On 05/05/2016 11:49 PM, Eli Zaretskii wrote:
> If we are going to use such kludges, why not specify fonts explicitly
> in the defface to begin with?  After all, that's what your patch
> attempts to do, albeit indirectly, right?

The patch I proposed basically implements the suggestions Stefan made in 
<http://bugs.gnu.org/19889#6> and <http://bugs.gnu.org/19889#24>. Stefan 
was responding to Glenn’s original bug report, which suggests that it is 
not a good idea for a face definition to specify a font explicitly, due 
to portability problems on systems lacking the font. See the attachment 
to <https://bugzilla.redhat.com/684797> for an example of how verbatim 
text in TeX mode was displayed as little black boxes because TeX mode 
specifies an explicit font on a platform lacking it.

I am by no means an expert on Emacs fonts or on font technology in 
general. That being said, I would like to fix this blocking bug, and 
Stefan’s suggestion was the only concrete one on the table. If the patch 
is problematic, then is there a better way to fix this bug? More 
specifically: is it the introduction of ‘fixed-pitch-serif’ that you’re 
objecting to, or the addition of FreeMono and Nimbus Mono L as fonts to 
look for, or is it something else? Is there some way we could make the 
patch less kludgy, while still addressing Glenn’s and Stefan’s concerns?