upgrading to multipath 0.4.9 presents incompatible config file changes

The priority checkers have been converted from individual binaries that callout to dynamically loaded libraries (dlopen). As a result, should a circa 0.4.8 config file remain in place, the priority checker becomes undefined, as that standalone path checker no longer exists. This will effect users who upgrade to Oneiric and users who upgrade from lucid to the next LTS.

One example of the format change is,

0.4.8:
prio_callout "/sbin/mpath_prio_alua /dev/%n"

0.4.9:
prio alua

There may be other config file changes, more exploration is needed.

Here's what the preconfigured, 0.4.9 priority checkers look like.

# echo 'show config' | multipathd -k | grep 'prio '| sort -u
  prio alua
  prio const
  prio emc
  prio hds
  prio hp_sw
  prio netapp
  prio rdac

In 0.4.8:
# echo 'show config' | multipathd -k | grep 'prio_callout'| sort -u
  prio_callout /sbin/mpath_prio_alua /dev/%n
  prio_callout /sbin/mpath_prio_alua %n
  prio_callout /sbin/mpath_prio_emc /dev/%n
  prio_callout /sbin/mpath_prio_hds_modular /dev/%n
  prio_callout /sbin/mpath_prio_hp_sw /dev/%n
  prio_callout /sbin/mpath_prio_netapp /dev/%n
  prio_callout /sbin/mpath_prio_rdac /dev/%n