This introduces some new helper functions which are exactly the same
as what we had before, but do not call
normaliseMixedAmountSquashPricesForDisplay, so that we can use the new
functions for displaying Transaction and Posting. It also goes through
and gets rid of most uses of the old showMixed* functions which would
benefit from using the new interface.
Transaction prices were being collapsed/misreported after close/open;
this is fixed. Now each separately-priced amount gets its own posting,
and only the last of these (for each commodity) gets a balance
assertion. Also the equity posting's amount is now always shown
explicitly, which in multicommodity situations means that multiple
equity postings are shown. The upshot is that a balance -B report
will be unchanged after closing & opening transactions.
