explicit fonts in specifier code?

[Ilya N. Golubev]

Your 2006-11-05 change of generic `specifier.c'
`specifier_instance_from_inst_list' added a very specific processing
of `matchspec', with retrieving charsets and other data from
`matchspec' just as it is done for font specifiers, one of many
specifier types.  It did not merely broke abstractedness of
`specifier.c' code.  It is very hard to predict how this change will
affect myriads of other uses of other specifier types, including
results of documented `specifier-matching-instance' calls for these
non- font specifiers.

If it will not change anything except font specifiers, then please add
comments explaining the following.

. How this is ensured. 

. Why it was actually generic `specifier_instance_from_inst_list' that
had to be changed.  So that could not put the desired processing in
`font_instantiate'.  (Or one or two more additional generic specifier
methods.)

Still better, please get `specifier_instance_from_inst_list' just as
generic as before, with all font specific data processing back in font
methods.

Never checked other recent changes of specifier code for this issue.