G19: Revisions to student loan data in the G.19

Starting with March 2009 numbers, data are revised to incorporate loans purchased by the Department of Education under the 2007-08 and 2008-09 Loan Purchase Programs. More information on these programs is available at http://federalstudentaid.ed.gov/ffelp/. In addition, with this release the "Federal government and Sallie Mae" sector is relabeled the "Federal government" sector to reflect that Sallie Mae completed its transition to a finance company in 2004. Sallie Mae's data before the completion of the privatization remains in the Federal government sector. This change affects the labeling solely and not the underlying data.