PluggableTextSpec>>font returns a default font if font is not specified.
This results in default font overriding any fonts in the plugged
textmorphs :-( as in the case of Help->FontSizeSummary. The exact font
to be used to render text should be determined lazily by textMorph and
not in pluggable text spec.
My proposed fix has a wide ranging effect, so I am posting it here for a
critique before finalizing a patch to Inbox.