softpipe: Handle adjacency primitives.
softpipe: Handle adjacency primitives.

Not fully tested.

Based on diagrams from
http://msdn.microsoft.com/en-us/library/windows/desktop/bb205124.aspx#Primitive_Adjacency

v2: Fix based on Brian's feedback.

Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>
Reviewed-by: Roland Scheidegger <7d58aee419d6f9201d75517c885374dff5e7d848@vmware.com>

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