bug#3174: NS: greek glyph rendering incoherent

[Jason Rumney]

Adrian Robert wrote:
> Greek, however, is still hosed, because emacs font backend core 
> decides these characters should be rendered using script "symbol".  I 
> don't know why, since it also knows about "greek", but it might be 
> because many Greek letters are used in both unicode categories.

The default fontset contains this definition for greek (from 
lisp/international/fontset.el):

    (greek ,(font-spec :registry "iso10646-1" :script 'greek)
       (nil . "ISO8859-7"))

charset-script-alist contains a suspicious looking (greek-iso8859-7 . 
latin), but that still doesn't explain why greek characters would get 
assigned to the symbol script.