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

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

Eli Zaretskii wrote:
> How did you get FreeSerif characters elsewhere in the buffer?  Which
> characters were those?

It was the other characters like "abc".  But I'm afraid I can't reproduce the 
effect now.  I've changed my default environment and perhaps that has affected 
things.

> What do you see for U+2E3F and U+20BD?

With 'emacs -Q' it's the same as in Emacs 24.4, namely, the Symbola glyphs.

> Anyway, does the idea of selectively removing codepoints from where we
> currently specify Symbola sound good, given these trials?

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. 
  Users will notice when the Symbola fonts make things worse for them.

Instead of using Symbola for all symbols, perhaps we should just use it for 
emoticons and other symbols known to be commonly bad.

It's too bad that we can't fall back on Symbola only when the font is missing 
the character.  I still don't understand things well enough to propose an 
implementation along those lines, though.