virt-manager: trying to fix runtime schema lookup error

The org.virt-manager.virt-manager schema is in
./result/share/glib-2.0/schemas/org.virt-manager.virt-manager.gschema.xml,
but virt-manager doesn't seem to pick it up:

  $ ./result/bin/virt-manager --debug
  /nix/store/gcd4wbaz1l1b4bf80b0drw8c1xd9m28j-virt-manager-0.10.0
  ----
  2013-11-03 20:50:39,180 (cliutils:75): virt-manager startup
  2013-11-03 20:50:39,180 (.virt-manager-wrapped:199): Launched as: ['/nix/store/gcd4wbaz1l1b4bf80b0drw8c1xd9m28j-virt-manager-0.10.0/share/virt-manager/.virt-manager-wrapped', '--debug']
  2013-11-03 20:50:39,180 (.virt-manager-wrapped:200): virt-manager version: 0.10.0
  2013-11-03 20:50:39,181 (.virt-manager-wrapped:201): virtManager import: <module 'virtManager' from '/nix/store/gcd4wbaz1l1b4bf80b0drw8c1xd9m28j-virt-manager-0.10.0/share/virt-manager/virtManager/__init__.py'>

  ** (.virt-manager-wrapped:16171): WARNING **: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files
  2013-11-03 20:50:39,394 (.virt-manager-wrapped:247): GTK version: 3.8.4

  (.virt-manager-wrapped:16171): GLib-GIO-ERROR **: Settings schema 'org.virt-manager.virt-manager' is not installed