- redenominate will use old_base if provided; instrument's currency otherwise 
   (instead of always using instrument's currency)
 - updated docs and NEWS
 - added tests


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/blotter/pkg/FinancialInstrument@1391 edb9625f-4e0d-4859-8d74-9fd3b1da38cb