Fix click suppression after dragend in cases where click doesn't fire.

Fixes Issue #1005 for both behavior.zoom and behavior.drag
More robust type inference for d3.interpolate.

Fixes #1180 #1179 #1176. Still a work in progress; needs a few more tests.
Favor strictEqual for testing.
Ignore null geometries.
Merge branch 'fix-interpolate' into 3.1.5
Merge branch 'fix-null-geometry' into 3.1.5
Merge branch 'fix-issue-1005' of https://github.com/appneta/d3 into 3.1.5
Redesign d3_eventSuppress slightly.
Merge branch '3.1.5'