the cluster strategy doesn't listen on the proper event type

[elemoine]

the cluster strategy listen on the map's zoomend event, instead it should listen to its layer's moveend event, to avoid cases where the strategy runs the clustering logic while the layer is invisible or out of range

[elemoine]

patch-1834-r8356-A0.diff is absolutely untested, and there for our cluster strategy bug finders to give it a try

depends on #1831 (not strictly)

[tschaub]

Feedback was  positive.

[tschaub]

register for events on the layer instead of the map

[tschaub]

Tests only pass with the patch for #1831. And, they only pass with the second patch. There is some weird behavior going on with event registration that causes tests to fail with the first patch.

The change to the Cluster test is a regression test against #1831. Tests pass with and without this change (given the changes to the cluster strategy). That, and the fact that the example still works are enough for me to say this is good to go.

[tschaub]

(In [8460]) Cluster strategy should register for moveend on the layer instead of zoomend on the map. p=elemoine,me r=me (closes #1834)