mongoexport problem on data with quotes

This is a regression from 2.6.x.

> db.artists.insert({ "name" : "Andy Warhol", "genome" :

{ "Pop Art" : 10 }

})
WriteResult(

{ "nInserted" : 1 }

)

> db.artists.insert({ "name" : "Quoted Andy Warhol", "genome" :

{ "\"Pop Art\"" : 10 }

})
Cannot use 'commands' readMode, degrading to 'legacy' mode
WriteResult(

{ "nInserted" : 1 }

)

> db.artists.find()
{ "_id" : ObjectId("5699157cc42b4297c59e8165"), "name" : "Andy Warhol", "genome" :

{ "Pop Art" : 10 }

}
{ "_id" : ObjectId("56991584c42b4297c59e8166"), "name" : "Quoted Andy Warhol", "genome" :

{ ""Pop Art"" : 10 }

}

> exit
bye

/tmp$ mongoexport --db test -c artists
2016-01-15T10:51:52.266-0500 connected to: localhost
{"_id":

{"$oid":"5699157cc42b4297c59e8165"}

,"name":"Andy Warhol","genome":{"Pop Art":10.0}}
2016-01-15T10:51:52.284-0500 Failed: json: error calling MarshalJSON for type bsonutil.MarshalD: cannot marshal [

{"Pop Art" 10}

]: json: error calling MarshalJSON for type bsonutil.MarshalD: invalid character 'P' after object key