Merge from vendor branch TNF:

Merge from vendor branch TNF:
Import ruby-spreadsheet-0.6.5.3 as math/ruby-spreadsheet.

The Spreadsheet Library is designed to read and write Spreadsheet Documents.
As of version 0.6.0, only Microsoft Excel compatible spreadsheets are
supported.  Spreadsheet is a combination/complete rewrite of the
Spreadsheet::Excel Library by Daniel J. Berger and the ParseExcel Library by
Hannes Wyss. Spreadsheet can read, write and modify Spreadsheet Documents.