Change Stage from defines to enums.
Serialize an operation that reaches a stage with STAGE_FLAG_ID_CONSTRAINT without a FID.

Without LU-543/LU-1331, the changelog record for an "mv foo1 foo2" command will not
include the FID of foo2. We get it from the database. However since we don't know
its FID, we have to get it from the database, which prevents us from inserting it
into the constraint engine on time. So we must wait until all the records before
it have cleared the pipeline before we can process it. Once the FID is recovered, it
can then be inserted into the constraint table, and normal processing can resume.
Added -lsost to list every file's OSTs.
Integrate remove_entry_from_stage into the only caller.
The stage is always locked when calling move_stage_entries, so remove the lock parameter.
Remove the entry_lock mutex.

Every time the entry_lock is taken, the stage mutex was also taken.
So taking entry_lock is redundant and will never block.