[COMMIT] Specify ERROR_ME_WARN explicitly in specifier_instance_from_inst_list().

[Aidan Kehoe]

 Ar an séú lá is fiche de mí Deireadh Fómhair, scríobh Stephen J. Turnbull: 

 > Aidan Kehoe writes:
 >  > 
 >  > Giacomo, in my local tests, this fixes the gnuclient problem you were
 >  > seeing. There is still a warning about the attempt to instantiate a
 >  > pixmap specifier on a TTY; this warning is probably wrong, and I’ll
 >  > fix it at some point, but this should be good enough for most purposes
 >  > now.
 > 
 > It's not obvious to me that the warning is wrong.  Pixmaps probably
 > "should" only be specified with a tag-set meaning "graphical display".

Mmm, and XLFD font specs “should” only be specified with a tag set meaning
“X11”; but that’s never been true and it is against the spirit of the
specifier API.

 > OTOH, it's reasonable for DWIM functions like specifier-instance and
 > set-specifier to try to do something about this. In the case of
 > specifier-instance, maybe it's OK to simply suppress the warning. 
 > set-specifier OTOH might want to helpfully add such a tag-set.

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