Introduce routines to manage thread credentials

fsal_save_ganesha_credentials should be called once to save
the Ganesha process's credentials.

fsal_set_credentials is called to set a thread's credentials
from the fsal_op_context_t.

Note that this sets fsuid, fsgid, and effective and filesystem
groups for Linux (Linux does not have separate egroups and fsgroups).

fsal_restore_ganesha_credentials is called to restore the
thread to Ganesha's process credentials.

Signed-off-by: Frank Filz <ffilz@us.ibm.com>

Conflicts:

	src/FSAL/access_check.c
	src/include/FSAL/access_check.h
Fix USE_DBUS-OFF build problems

Not enough of the dbus interface was ifdef'd out...
This leaves the client manager and export manager infrastructure
untouched so it is available for other uses.

Note: stats are still gathered, you just can't get them out without
dbus.  Also, an ifdef in nfs4_Compound.c was just commented out.  This
is left as a marker until the old stats code has been removed.

Signed-off-by: Jim Lieb <jlieb@panasas.com>
Merge remote-tracking branch 'linuxbox2/next' into cthon13_merge
Merge remote-tracking branch 'ffilz/2.0-set-thread-creds' into cthon13_merge