dirauths write corrupted keypin journal

When starting my dirauth, I see this line:

[warn] Loaded 56168 entries from keypin journal. Found 5 corrupt lines, 0 duplicates, and 15814 conflicts.

I assume the corrupted lines happen because the file is not atomically written, so if the disk runs full (which occasionally happened in the past due to bwauth issues) we're corrupting the log.