Add pinch-to-zoom support for Android.
brush.clamp: return null if there are no scales.

Similarly, if there are no scales, setting a clamp does nothing.

For consistency with brush.extent.
Fix transition.selectAll with null nodes.
Fixes for non-orderable values.

In addition to NaN, which is not equal to itself, you can have objects that are
not orderable due to defined valueOf functions which return NaN. For example:

  var o = new Number(NaN);

Here, o == o is true, but o <= o is false. Therefore it was possible for d3.min,
d3.max and d3.extent to observe these non-orderable values rather than ignore
them as intended. The fix is to check !(o <= o) rather than o == o.

This commit also fixes d3.bisect when the search value is non-orderable.
Previously, bisectLeft returned lo for non-orderable values, and bisectRight
returned hi. However, if the search value is non-orderable, then this return
value does not satisfy the conditions of bisection. This commit changes the
bisection methods to return NaN when the search value is non-orderable.

As a side-effect, the fix to d3.bisect now causes d3.scale.threshold to return
undefined when passed a non-orderable value, such as undefined. (Previously, a
threshold scale would return the highest value in the range, because it used
bisectRight internally.)
Slightly shorter.
Return undefined, not NaN.

Since the quantile scale allows arbitrary values in the range, there’s no reason
the return value for unorderable input needs to be a number.
Restore undefined behavior for d3.bisect.

Rather than return NaN, this change restores the previous undefined behavior
when an unorderable value is used for bisection. After discussing with Jason, I
think this is more consistent given that d3.bisect also requires that the input
array is sortable, and therefore only contains orderable values. Thus, it is the
responsibility of the caller to check that the search value is defined before
doing bisection, and so this commit fixes the threshold scale rather than the
bisect method. (Also, this is consistent with the existing quantile scale.)
Don’t mask private variable.
Merge branch 'fix-transition-selectAll-null' into 3.2.1
Merge branch 'brush-clamp' into 3.2.1
Merge branch 'zoom' into 3.2.1
Merge branch '3.2.1'