FreeNAS Code

Destroying volumes could leave the database in inconsistent state if there were ZVols currently in use.
Also handle the export of volumes without cascade works as expected

Wipe disks before using.

Fix for LDAP slider, possibly fixes ticket #723 as well.

fix code indent

restart istgt instead of try to reload

fix bug on replace in-place (wrong pool name)

use zpool id to import

Don't automatically chown unknown mountpoints to root:wheel in the event
the user/group cannot be resolved on the FreeNAS box.

This can create undesirable side effects (in particular with NFS) if the
FreeNAS and client instance user/group list are out of synch and someone
logged into the box and changed the user/group to an 'unknown'
user/group (chown(2) allows numeric assignment anyhow -- for better or for
worse -- and chown(1) allows numeric / name based assignment).

This should be handled via Exceptions in the future, but for now
defaulting to root:wheel in the GUI alone is good enough.

Document the behavior accordingly.

1. Drop unnecessary 'r' open mode flags.
2. Use ContextSuites instead of ad hoc open->read/write->close.

Style changes.