pnfsmanager: Change defaults for pnfsmanager

Enables folding and full path permission check. Increases default thread
count to 12 (tests I ran years ago showed that Chimera scales well until
at least 12 threads - on modern hardware it may scale even better).

Note that full path permission check may result in access to files and
directories that was allowed before now to be denied. Sites are adviced to
check the permission settings on directories on upgrade, or to disable
the POSIX compliant full path permission check by flipping the property
pnfsmanager.full-path-permission-check.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Karsten Schwank <karsten.schwank@desy.de>
Patch: http://rb.dcache.org/r/5771/