In FileOp/FileBackend:

In FileOp/FileBackend:
* Added SHA-1 to FileOp::attemptBatch $predicates (since concatenate was removed from FileOp). This lets us get rid of temp file backups, as the remaining failure case is just the backend medium going down (the ops would break in that case anyway). Doing so reduces RTTs and backup file I/O overhead. This also simplifies expiry object support by avoiding having to stash the expiry values of temp backup objects somewhere.
* Improved precheck() and attempt() status logic in FileOp::attemptBatch() a bit. Use separate $subStatus var to check if each op is OK.
* A few minor code cleanups and comment tweaks.
* Fixed MoveFileOp bug found in unit tests when the source/dest are the same and an overwriteDest/overwriteSame param is given (the file would just get deleted). Improved CopyFileOp in this case too.
Other:
* Added more unit tests.