If we write the annotation but not the microdescriptor, rewind.

This fixes bug 9047 (and some parts of 9031, 8922, 8883 that weren't
fixed in 8822).  Bugfix on 0.2.2.6-alpha.
Define SEEK_SET for platforms that lack it.
Merge branch 'bug9047' into maint-0.2.4
Merge remote-tracking branch 'origin/maint-0.2.4'