Fix foreign currency income/expense transactions in reports.

Since commit 9fc583d3 was added as a
fix for some currency conversions performed in reports income/expense
transactions which involved a currency conversion were not properly
displayed in the transactions by account report.

Extended the multi-currency report testcase to catch this error and
fixed the problem by resurrecting some conversion code which was
removed by that commit, but moved it to a place where it's applied
only to income/expense transactions.

BUG: 345550
REVIEW: 123154