The new analyzeField() helper func is used for both regular fields and
for composite fields.
With this change, all analysis is done up front, for both regular
fields and composite fields.
After analysis, this change counts up all the row capacity needed and
extends the AnalysisResult.Rows in one shot, as opposed to the
previous approach of dynamically growing the array as needed during
append()'s.
Also, in this change, the TermFreqRow for _id is added first, which
seems more correct.
