Build target to wrap dist/install in a .deb archive.

Build target to wrap dist/install in a .deb archive.

Adds "make deb", which does a "make dist" build and wraps the
resulting dist/install files in dist/xen-<version>.deb

This is _not_ a "packaged" version of Xen for Debian users, nor is it
intended to compete with anyone else's packaging efforts.  In
particular it doesn't do any of the boot-time or fstab fixups needed
to actually start the xen tools.  It's just a quick hack for
developers to be able to quickly install and uninstall a Xen build on
a test box.

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>