[HarfBuzz] variation selector support

[Behdad Esfahbod]

Done.  Please test.

On 06/02/2010 07:59 PM, Jonathan Kew wrote:
> Hi Behdad,
> 
> There seems to be a problem with the variation-selector support in hb_map_glyphs(); it doesn't account for the fact that the VS slots need to be eliminated from the buffer during char-to-glyph mapping. As a result, we end up with .notdef glyphs corresponding to the VS codepoints, even though the correct variants are chosen for the base characters.
> 
> The attached patch ought to fix this.
> 
> JK
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