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
Tidy up the vchan test script and make it loop.

Also add simple xenstore initialization scripts to setup the
/conduit space for coordinating a vchan server
Merge pull request #51 from avsm/master

Tidy up the vchan test script and make it loop.
Make the ENDPOINT module type not explicitly depend on Vchan

We do this by making `port` an abstract type that is substituted
in from the functor applications.
Add another `port` -> `Vchan.Port.t` alias
Merge pull request #52 from avsm/master

Make the ENDPOINT module type not explicitly depend on Vchan
Shift the Xen-specific OPAM dependencies out to depopts
Merge pull request #53 from avsm/reduce-deps

Shift the Xen-specific OPAM dependencies out to depopts
Do not enable xenctrl unless xen-evtchn is also installed
remove a bashism in the configure script
Merge pull request #54 from avsm/master

Do not enable xenctrl unless xen-evtchn is also installed