This patch makes a number of changes to enable content-type
metadata to be updated when using the fast-POST mode of
operation, as proposed in the associated spec [1].
* the object server and diskfile are modified to allow
content-type to be updated by a POST and the updated value
to be stored in .meta files.
* the object server accepts PUTs and DELETEs with older
timestamps than existing .meta files. This is to be
consistent with replication that will leave a later .meta
file in place when replicating a .data file.
* the diskfile interface is modified to provide accessor
methods for the content-type and its timestamp.
* the naming of .meta files is modified to encode two
timestamps when the .meta file contains a content-type value
that was set prior to the latest metadata update; this
enables consistency to be achieved when rsync is used for
replication.
* ssync is modified to sync meta files when content-type
differs between local and remote copies of objects.
* the object server issues container updates when handling
POST requests, notifying the container server of the current
immutable metadata (etag, size, hash, swift_bytes),
content-type with their respective timestamps, and the
mutable metadata timestamp.
* the container server maintains the most recently reported
values for immutable metadata, content-type and mutable
metadata, each with their respective timestamps, in a single
db row.
* new probe tests verify that replication achieves eventual
consistency of containers and objects after discrete updates
to content-type and mutable metadata, and that container-sync
sync's objects after fast-post updates.
[1] spec change-id: I60688efc3df692d3a39557114dca8c5490f7837e
Change-Id: Ia597cd460bb5fd40aa92e886e3e18a7542603d01
e91de49d68