Fixed interactive gridlines to take into account brush when drawing points on stacked area chart

[SpencerWie]

Currently the drawn points on the interactive grid line of a Stacked Area Chart do no take into account when using brush on a StackedAreaWithFocusChart. The line chart does not have this issue, the code that corrects this in the line chart is absent for stacked area chart.

This change simply adds the logic that was done for the line chart:

nvd3/src/models/lineChart.js

Lines 290 to 299 in 254bb45

	var extent = focus.brush.extent() !== null ? (focus.brush.empty() ? focus.xScale().domain() : focus.brush.extent()) : x.domain();
	var currentValues = series.values.filter(function(d,i) {
	// Checks if the x point is between the extents, handling case where extent[0] is greater than extent[1]
	// (e.g. x domain is manually set to reverse the x-axis)
	if(extent[0] <= extent[1]) {
	return lines.x()(d,i) >= extent[0] && lines.x()(d,i) <= extent[1];
	} else {
	return lines.x()(d,i) >= extent[1] && lines.x()(d,i) <= extent[0];
	}
	});

Into the StackedAreaChart.

To see this issue go to the example:

https://rawgit.com/novus/nvd3/master/examples/stackedAreaWithFocusChart.html

Then move the pan to all the way to the left. The dots on the grid line will match up, panning to the right will cause an ever growing offset of the drawn dots.

To check that the issue is fixed build this version and go to the same example: /nvd3/master/examples/stackedAreaWithFocusChart.html.