Fix for some redundant points on resampling.

Also restore path.area and add a few tests.
Fix for clipping losing `this`.
Checkpoint improved clipping.

Passes spiral test.
Merge branch 'projection' into projection-clipAngle

Conflicts:
	d3.v2.js
	d3.v2.min.js
	src/geo/circle.js
	src/geo/projection.js
Fix a few bugs.

Hurrah for tests!
Remove unused code.
Fix missing interpolated point.
Remove unused code.
Use linear interpolation for longitude.
Merge remote-tracking branch 'mbostock/projection' into projection

Conflicts:
	d3.v2.min.js
Revert "Use linear interpolation for longitude."

This reverts commit b6d7c5e49e72e638462fecf1c33eee44f31700e7.
Merge remote-tracking branch 'mbostock/projection' into projection

Conflicts:
	d3.v2.min.js
Lower threshold for linear interpolation.

Interpolation of longitudes becomes inaccurate near the poles, since
they become mathematically insignificant in relation to a sphere.
However, for map projections, we want to interpolate longitudes even at
the poles themselves, since many projections distort the poles along an
edge.
Revert fix from previous commit.

It was breaking obviously in the resampling demo.

Retains a minor optimisation.
Fix circle.clip.

Polygon LinearRings weren't being closed correctly.
Reduce threshold for linear interpolation (again).
Avoid generating coincident points.

This was breaking antemeridian clipping in some rare cases where a point
was coincident with the antemeridian.
Fix anomalies.

The antemeridian interpolator was mistakenly assuming longitudes of
interpolation points are exactly on the antemeridian. An alternative fix
would be to use exact equality tests for the coincident points test, but
it feels safer to use a margin of error.
Add extra ring when polygon subsumes clip circle.

This can be optimised using the 3D coordinates directly from the
rotation step, rather than performing additional trig. calculations.
Merge pull request #837 from jasondavies/projection

Add extra ring if polygon "surrounds" clip circle.