Change AccountingTransaction_isDestination/SourceCurrencyConvertible so that conversion tab is always visible when conversion is set on lines, even if the resource is the same as the section's accounting currency.
Change accounting workflow to refuse validation of a transaction if conversion is set on lines (to a value different from quantity) when it should not be.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@23717 20353a03-c40f-0410-a6d1-a30d3c3de9de