r13244: Allow control of the location of the Samba3-compatible winbindd pipe

r13244: Allow control of the location of the Samba3-compatible winbindd pipe
in Samba4.  This allows us to start winbindd by default, including in
'make test'.

This is via a new 'winbindd socket directory' parameter for utilities
linked against loadparm, as well as a --with-winbindd-socket-dir
option to configure (setting the default and the value for simple
clients).

I hope to add basic winbindd tests, to ensure continued correct
operation, but at least now I don't have to manually change my 'server
services' line.

The other problem with the hard-coded /tmp/.winbind is that RedHat has
moved this in Fedora (to /var/run I think).  For this reason, this
functionality should probably be ported to Samba3 as well.

The default for Samba4 is PREFIX/var/run/winbind_pipe.

I have also re-added the paranoia checks from Samba3 for correct
permissions on the socket directory.

Andrew Bartlett