[PATCH] CTDB recovery lock cleanups

[Martin Schwenke]

I'm in the process of generalising the code that checks the recovery
lock when the main CTDB daemon sets the recovery mode to normal.  This
code will then be used to:

1. Test the recovery lock when setting recovery mode to normal (as now).

2. Take the recovery lock during recovery - this will be asynchronous,
   so will no longer block if the cluster filesystem is slow.

3. Split the recovery lock into a recovery lock, held only during
   recovery, and a cluster lock to be held by the master node.  This is
   part of the general task of untangling cluster management from
   database recovery.

Instead of only using a fcntl(2) lock on the cluster filesystem, a
configurable helper will be used to take any type of cluster
mutex.  Well, any type for which a helper can be written...  :-)

I'm going to post this in a few chunks to make it easier to review.

Attached are some initial clean-ups of the recovery lock code that make
writing the rest of the code easier.

Please review and push...

peace & happiness,
martin
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