JsonLoader: field values get out of order when fieldname key is repeated

while working on a test for SOLR-5183 i discovered a bug in the way field values are ordered when the fieldname key is repeated.

ie, these two docs should wind up having identical values for the field "f", but currently the order of the values gets swapped in doc #2...

{"add":[
   {"id":"1", 
    "f":[45,67]
   },
   {"id":"2", 
    "f":45,
    "f":67
   }
]}