Cludge around our hasLayer implementation to make us work with the latest Leaflet master. Fixes #159

Our hasLayer returns true when we contains a marker. FeatureGroup/LayerGroup (which we inherit from) now check hasLayer when addLayer is called. At this stage our hasLayer will return true, stopping the marker from ending up on the map.
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Add a real world example that shows a bug.
Fix IDs in example data.
Make this work on old leaflet too. Thanks @nkovacs
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Merge pull request #162 from skullbooks/master

Add an example that shows some strange error with a disappearing marker.
Move example to old-bugs dir (not that it is fixed yet)
Fix clearLayers with spiderfied markers. Refs #162
Remove hasProperty checks from loops. Refs leaflet/leaflet#1606
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