GeoPointFieldMapper doesn't merge GeoPoint specific properties

[kzwang]

# add mapping
curl -XPUT localhost:9200/test/test/_mapping -d '{
  "test": {
    "properties": {
      "testGeo": {
        "type": "geo_point",
        "validate": false
      }
    }
  }
}'

# update validate to true
curl -XPUT localhost:9200/test/test/_mapping -d '{
  "test": {
    "properties": {
      "testGeo": {
        "type": "geo_point",
        "validate": true
      }
    }
  }
}'

After update, the validate is still false and no exception is thrown. Other fields like store etc. works.