ObjectStore: fix Transaction encoding version number

ObjectStore: fix Transaction encoding version number

dbae92253f6bf64431cdb28e5e5be41260de5aea changed the encoding
significantly, but did not increase the transaction encoding version.
To fix this:
1) Increment the version number to 9.
2) Due to this bug, there are versions which encode the version 9
encoding incorrectly with version 8.  We will detect those by trying to
first decode any version 8 encoding with the old decoding function, and
then trying with the new one if there is an exception.

Fixes: 10734
Signed-off-by: Samuel Just <sjust@redhat.com>