Bug 565656 – Add marks to scales

        * gtk/gtkrange.[hc]: Add internal api to define 'stop values'
        that have a little resistance when dragging the slider over it.

        * gtk/gtk.symbols:
        * gtk/gtkscale.[hc] (gtk_scale_add_mark): New function to add
        a 'mark' to a scale, which will draws a tick, plus optionally
        some text, and makes the value a stop value.
        (gtk_scale_clear_values): Removes all marks.

        * tests/testscale.c: Test for marks on scales
        * tests/Makefile.am: Integrate it


svn path=/trunk/; revision=22149