prefix as the installed libvirt, use the same localstatedir /var
  (instead of /usr/var) and sysconfdir /etc (instead of /usr/etc) to
  be able to connect to the system daemon, and use the system local
  options
* src/xs_internal.c: avoid error message when non-root cannot open
  xenstore
* src/xend_internal.c: avoid error message when non-root cannot
  directly access xend, in those 2 cases the proxy (or remote code)
  should implement the access so there is no need to raise the error
  there.
Daniel