Kill another 7% from Pango

[Federico Mena Quintero <federico ximian com>]

Hi,

One thing we discussed on #performance once was that using
G_TYPE_INSTANCE_GET_PRIVATE() could be making critical code slower than
needed; this is because that macro causes lookups in the type system.

I took some profiles, and filed this:

http://bugzilla.gnome.org/show_bug.cgi?id=322174

The result is to shrink pango_fc_font_get_glyph() from 8.37% down to
1.31% on pango-language-profile.

Could someone please review the patch attached to the bug?

Thanks,

  Federico