Branch b_release_1_4_6

Branch b_release_1_4_6
Use (effectively) ptlrpc_daemonize() when starting the ping evictor thread,
as this thread can do filesystem IO when evicting clients (update last_rcvd)
and as a result trip LASSERT in pop_ctxt().

We can't call ptlrpc_daemonize() directly from code in obdclass as that
results in module symbol circular dependencies.  Looking into moving the
pinger code into ptlrpc entirely to avoid this issue.
b=9961
r=nathan