Change all usage of xaccTransSetDatePostedSecs to xaccTransSetDatePostedSecsNormalized.

In fact, all calls to this setter refer to the plain date and not to
any time-of-day. Consequently, only the normalized setter must be used
everywhere. (Subsequently, the previous setter could be removed, as
it turned out to be not used anywhere, but that's another story.)

As a side effect, this makes the register2 set the PostedDate in the
same way as the old register again. The register2 used to introduce a
time-of-day part in the PostedDate, but this should not be done. Only
the EnteredDate has a time-of-day part.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23045 57a11ea4-9604-0410-9ed3-97b8803252fd