In saveInstruments, 'pos' should 'FinancialInstrument:::.instrument' (reverts to r1475)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/blotter/pkg/FinancialInstrument@1619 edb9625f-4e0d-4859-8d74-9fd3b1da38cb