git: Disable HAMMER live dedup, mark as experimental

[Thomas Nikolajsen]

>commit 6de803f0514ff0019181d026a825d1e8a9a4c404
>Author: François Tigeot <ftigeot at wolfpond.org>
>Date:   Wed Jan 18 10:36:56 2012 +0100
>
>    Disable HAMMER live dedup, mark as experimental
>    
>    * Comment out mentions to it in the hammer(8) manpage
>    
>    * Live-dedup is a relatively new feature that has not undergone
>      extensive testing.
>    
>    * It may have some issues with HAMMER bigblocks, we do not want
>      users to run it on production machines yet.
>..
>-SYSCTL_INT(_vfs_hammer, OID_AUTO, live_dedup, CTLFLAG_RW,
>-          &hammer_live_dedup, 0, "Enable live dedup");
>+SYSCTL_INT(_vfs_hammer, OID_AUTO, live_dedup, CTLFLAG_RD,
>+          &hammer_live_dedup, 0, "Enable live dedup (experimental)");

Any special reason to turn vfs.hammer.live_dedup sysctl to R/O?
(I haven't noticed a tunable to turn it on; only way is to change code)

Do we have any known problem with live_dedup?
(I haven't noticed a bug on this in our bug handling system)

Live_dedup was off by default;
which seemed fine for an experimental feature.

 -thomas