Merge pull request #49 from avsm/master

Add the start of a Mirage regression test (use build.sh)
xen: unmask event channels on listen and connect

The new mini-os is careful to create the channels masked.
We must therefore unmask them before we can use them.

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge pull request #50 from djs55/fix-xen-events

xen: unmask event channels on listen and connect