xen: add constraint 'type id = string' to match unix

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #2 from djs55/xen

xen: add constraint 'type id = string' to match unix
Bump to 1.0.1 for the xen bugfix
Merge pull request #3 from avsm/master

Bump to 1.0.1 for the xen bugfix