setIcon with DivIcon no longer works after setIcon icon reuse change

[danzel]

As of #1726 you cannot use setIcon and pass a new DivIcon. If you do the icon doesn't end up getting updated.
This breaks MarkerCluster which relies heavily on DivIcon.

Refs Leaflet/Leaflet.markercluster#190

[mourner]

@danzel had to rewrite this code a bit because of #1768, could you please check if the use case described here still works?

[danzel]

Yep, still works.
Added another test case to make sure we are getting icon/shadow element reuse.

[mourner]

Awesome, thanks Dave!