Comment 55 for bug 365065

Writing it is enabled in https://github.com/Gnucash/gnucash/commit/0871866c3882b99cadadd63c71b8a23220060a64. It will be called every time the transaction is entered manually, but won't be called for imports or SX.

It's also a bit of a hack and not really necessary. Date/times are stored as iso dates (e.g. 2014-07-03 08:03:20 Z), so we're totally free to replace the internal representation. Since date_posted is always just a date, we can just stop using timespecs (which I intend to do anyway as part of converting from gdate to boost::calendar) and treat date_posted as a date instead of a time.