Add hasLayer to LayerGroup
Add the method hasLayer to LayerGroup, return false when not present or checking for a null layer.
Fix js typo
hasLayer not checking for null
Return false when checking for a null object in L.Map.hasLayer, in
response to issue #1282.
Merge pull request #1302 from rvlasveld/fix_hasLayer_check_for_null

hasLayer not checking for null
Merge pull request #1300 from rvlasveld/add_hasLayer_to_layerGroup

Add has layer to layer group
update build and changelog