Fix missing d3.transition in IE. Fixes #1491.

IE doesn’t support __proto__ patching, so if the selection.prototype.transition
method isn’t yet defined at the time d3_selectionRoot is defined, it won’t
inherit the method when the prototype is patched later! This restores the
original order of dependencies so that the transition method is defined before
d3_selectionRoot is created.
Merge branch 'master' of https://github.com/mbostock/d3