[gtkmm] New pangomm interface issue

[Naofumi Yasufuku <naofumi yasufuku net>]

Hi,

In gtkmm-1.3.22, some pangomm interfaces have been changed, and so
I'm faced with some problems.

I want to call Pango::Font::get_matrics() with NULL language argument
to indicate to get the metrics for the entire font.
But I cannot do it because new interface requires a const reference to
Language.

pango C API allows pango_font_get_metrics(font, NULL), but pangomm
doesn't allow it.

I think Pango::Font should provide 

  FontMetrics Font::get_metrics()
  {
    return FontMetrics((pango_font_get_metrics(gobj(), 0)));
  }

to support pango C API specification completely.

There are same problems with other Pango:: classes. For example,
pango_font_description_better_match(desc, NULL, new_match) can be
called to determine if the style attributes of new_match are a match at
all, but Pango::FontDescription doesn't provide such interface.

I think pangomm interfaces should be considered more carefully to
support C API specification faithfully.

Regards,
--Naofumi