wrong position of underline

[Changwoo Ryu <cwryu adam kaist ac kr>]

A multibyte bug.

When I set LANG=ko and specify fontset in gtkrc, underline of label is
placed at a wrong x coordinate.

It looks that gtk_label_process_row() in gtk/gtklabel.c assumes that a
text width is sum of its one byte characters' widths.  I couldn't
understand the code...  But I think there's no need to call
gdk_text_extents for every bytes.