Depend on mirage-profile to add tracing support

- Report time spent in caml_minor_collection and block_domain.
- Label Xen event channel threads.
- Label threads waiting for XenStore.
- Label sleep threads.
Merge branch 'profile' of git://github.com/talex5/mirage-platform

Conflicts:
	CHANGES
	xen/_vars
resolve merge conflict in CHANGES