Primitive restart: Test in every possible draw mode.

Some implementations (i965 in particular) treat primitive restart
differently depending what type of primitive is being drawn.  This
test verifies that primitive restart works correctly for all primitive
types.
WIP: start testing GS in/out types
WIP: fix shader_runner error reporting when vertex data included.
WIP: Basic test of GS input varyings
Geometry shaders: add a basic EndPrimitive() test.
WIP: large EndPrimitive test