Rename volume_export to volume_detach to be more generic [1].
More 'renaming' needs to occur, but this will be an 8.2+ thing, not an 8.0.3 thing (this is being done to avoid thrashing dlavinge).
Mash zfs_export into volume_detach because it was only one command.
Iterate through commands in a loop and stop at any errors to ensure that things can be cleaned up at a later point in time if something fails.
Document desired behavior and requirements.
1. Requested by jpaetzel.
Authored by: yaberauneya 2011-12-27
Parent: [r9317]
Child: [r9319]
