Shift refresh of mirror table right into monitor_dev_for_events().
Use !vg_write_lock_held() to recognize use of lvchange/vgchange.
(this shall change if this would no longer work, but requires
futher some API changes).
With this patch dm mirror table is only refreshed when necassary.
Also update WARNING message about mirror usage without monitoring
and display LV name.
git://sourceware.org / lvm2.git / commit