Previously, procfs would consider all processes that have a non-free
kernel slot *or* an in-use PM slot. However, since AVFS, a non-free
kernel slot does not imply an in-use PM slot. As a result, procfs
may use PM slots that have a zero PID value. If two such entries are
present in the retrieved PM table, procfs would try to add two inodes
with the same name "0", triggering an assertion in vtreefs.
This patch makes procfs consider only the PM slot for (non-task)
processes.