- Specifier improvements for support of specifier inheritance
  (necessary for the new font mapping API).

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Specifier changes
-----------------

'Fallback should be a locale/domain.

(get-specifier specifier &optional locale)

#### If locale is omitted, should it be (current-buffer) or 'global?
#### Should argument not be optional?

If a buffer is specified: find a window showing buffer by looking
- at selected window
- at other windows on selected frame
- at selected windows on other frames in selected device
- at other windows on ""
- at selected windows on selected frames on other devices in selected
  console.
- other windows sel from other devices sel con
-      ""       oth       ""           sel
- sel win sel from sel dev oth con
- oth win sel from sel dev oth con
- sel win oth from sel dev oth con
- oth win oth from sel dev oth con
- sel win sel from oth dev oth con
- oth win sel from oth dev oth con
- oth win oth from oth dev oth con

If none, use  buffer -> sel from -> etc.

Returns multiple values
  second is instantiator
  third  is locale containing inst.
  fourth is tag set

(restart-specifier-instance ...)

like specifier-instance, but allows restarting the lookup, for
implementing inheritance, etc.  Obsoletes
specifier-matching-find-charset, or whatever it is.  The restart
argument is opaque, and is returned as a multiple value of
restart-specifier-instance.  (It's actually an integer with the low
bits holding the locale and the other bits count int to the list)
attached to the locale.)
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