This patch will make xm return a exit code of 3 if `xm list
<non_existant_domain>` is done rather than the generic code of 1. I
used 3 because XendClient had a macro setup pointing
ERROR_INVALID_DOMAIN to 3.
From: "Shaun R." <mailinglists@unix-scripts.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>