This fixes issue #1127. In my understanding, PR #552 was meant to fix
this, but was incomplete.
Without this patch, automated transactions are invisible to
assertions.
This patch fixes this by adding a flag to the account to tell it that
there is a new posting, analogous to the behavior of finalize().
I dug up issue #1127 too late to find that this is the same solution
proposed by @tbm. Although I wrote this independently, credit goes to
Martin Michlmayr (@tbm).
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