Fix quick zoom in/out in firefox making everything disappear. Fixes #140 Fixes #272
Slow the animation down, looks better :)
Fix some cases where zoomToShowLayer wouldn't work. Fixes #286 #228 #203
Update change log, bump to 0.4.0 and rebuild
Reverted MarkerClusterGroup before pull
Merge branch 'master' of https://github.com/Leaflet/Leaflet.markercluster

Conflicts:
	dist/leaflet.markercluster-src.js
	dist/leaflet.markercluster.js