bug#20727: 24.5; Font fallback doesn't work for the Emoji range

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

Eli Zaretskii wrote:

>> After trying it a bit I'm worried that this will be flaky.  Often the Symbola
>> fonts are better (much better, if the default fonts lack the symbols), often
>> worse (if both fonts have the symbols), and it all depends on a lot of settings.
>
> What settings are those?  The only ones I think are relevant are the
> default fontset and the default font.  Are there any others?

I'm not sure, but I found that my ~/.emacs file, at the end, said 
"(custom-set-faces)" -- something I didn't put in there, but I suppose I ran 
"customize" at some point in the unremembered past, though I don't remember ever 
customizing fonts.  I suppose the settings installed by custom-set-faces, 
whatever they are, alter the fonts installed by the recent change, and this 
messes up my testing.  (Possibly they saved faces calculated *before* the recent 
change to Emacs, and custom-set-faces is trying to restore them?)  I will 
comment out the customization code before doing further testing, but these are 
the sorts of glitches that I fear will affect other users.

I took a look at your recent commit 2f09f8952489b5c90488faf66f71a4252aed5c2c and 
things are better on Ubuntu, thanks.  In my default environment it now uses the 
fixed font so the Symbola stuff doesn't get in the way.  I'll try it out on 
Fedora in a couple of days.

I did try it with emacs -Q to get the Ubuntu 15.04 default font (Ubuntu Mono), 
and found that recent Emacs in many places looks nicer and in some places not as 
good.  Focusing on the latter:

U+201F DOUBLE HIGH-REVERSED-9 QUOTATION MARK now displays as 
xft:-unknown-Symbola-normal-normal-semicondensed-*-17-*-*-*-*-0-iso10646-1 
(#x39B) which is spidery, whereas it formerly displayed as 
xft:-unknown-FreeMono-normal-normal-normal-*-17-*-*-*-m-0-iso10646-1 (#x8A8) 
which is more legible.

U+204F REVERSED SEMICOLON has a similar problem.

U+2047 DOUBLE QUESTION MARK
U+2048 QUESTION EXCLAMATION MARK
U+2049 EXCLAMATION QUESTION MARK
are too large in Symbola; the old FreeMono version was better.

The currency symbols look worse than before: they used to be constant-width 
(most of them anyway) and matched Ubuntu Mono better.  Perhaps we should leave 
them alone?

Thanks for doing all this -- it must have taken you quite some time.