Enabling a commented-out function,

        * gdk-pixbuf/gdk-pixbuf.defs (gdk_pixbuf_new_from_xpm_data_interp):
        New function.
        * gdk-pixbuf/gdk-pixbuf-support.c, gdk-pixbuf/gdk-pixbuf-support.h:
        New files.
        * gdk-pixbuf/Makefile.am (libguilegdkpixbuf_1_2_la_SOURCES): Add them.