Ceph

The ECBackend needs to use the TPC protocol outlined in ec_overwrites.rst based on the FLAG_EC_OVERWRITES flag. That is, with that flag set, ECBackend will use a write-aside object prepare/commit process with the append-only implementation so that we can get some testing before the rest of the implementation is ready.

The first step is to write an explicit state machine using the dot language for the TPC mechanism incorporating all of the relevant steps and update the doc build process to stick a rendered version into the docs (see the peering state machine).