This fixes a bug in r14495. The bug is that auto-completed transactions
aren't correctly marked as pending. This bug is probably responsible for
the crashes like those in bug #348469.
In general, the register makes it very difficult to consistently
distiguish between beginning to edit a transaction that's being edited
in another register and beginning to edit the blank transaction,
which is already open for editing, but isn't marked pending so that
we can pretend it hasn't been opened if it never gets modified.
Fortunately, the auto-completion code only runs on the blank transaction,
so we can assume it's not being edited in another register. This patch
goes ahead and marks the blank transaction as pending.