FieldLookup for field with multiple values

[Matt Honeycutt]

It seems that the StringIndex returned by
FieldCache.Fields.Default.GetStringIndex() only indexes one value for a
document even when the document has multiple values for the field.  Is there
a performant want to get all the values for a particular field in a
ScoreDoc?  I'm having to do this across the entire result set of ScoreDocs
(up to 50,000), and retrieving the values through LuceneDocument.GetFields
is not going to cut it.