Maintain a count of the number of suspended devices in libdevmapper

Maintain a count of the number of suspended devices in libdevmapper
and use this for the LVM critical section logic.  Also report an error if
code tries to load a table while any device is known to be in the
suspended state.
(If the variety of problems these changes are showing up can't be fixed
before the next release, the error messages can be reduced to debug
level.)