Add another type multi_field for mapping to support mapping more than one core type. This is handy, for example, to map the same string type, once analyzed and one not_analyzed. For example:

{
    person : {
        properties : {
            "name" : {
                type : "multi_field",
                "fields" : {
                    "name" : {type: "string", index : "analyzed", store : "yes"},
                    "not_analyzed" : {type: "string", index : "not_analyzed"},
                }
            }
        }
    }
}

The above example, the name mapping is a multi field mapping. The name within the multi_field mapping is the "default" mapping (and used as if it was mapped regularly). The not_analyzed name is accessed through name.not_analyzed, and it won't be analyzed.

A special case is when merging, upgrading core type mapping into multi field mapping if the new mapping set for this property is now multi mapping.