Revision 1:
  Use the format_dev_t function for target status functions.

Revision 2:
  When multiple load ioctls are issued the reference count on older
  'new_tables' wasn't being dropped.  [Christophe Saout]

Revision 3:
  Move retrieve_status up so dev_wait() can use it.

Revision 4:
  dev_wait was meant to return table status not dev status.  [Alasdair Kergon]

Revision 5:
  Fix error message when linear targets gets handed more than 2 arguments.
  [Alasdair Kergon]

Revision 6:
  Support an arbitrary number of target parameters.  [Alasdair Kergon]

Revision 7:
  Import the 2.4 version of dm-io

Revision 8:
  port dm-io to 2.6

Revision 9:
  MOre snapshot porting.

Revision 10:
  Add a new target method that allows the target to intercept io
  completion.  In addition context may be passed between the targets map
  function and the targets endio function.

Revision 11:
  more porting

Revision 12:
  more porting

Revision 13:
  more porting

Revision 14:
  more porting

