An accessor for the content of a resource.
All Resource objects which represent resources in a
Repository must implement this interface. A user of the resource can
then cast the Resource object to this type and then obtain an
InputStream to the content of the resource.
Returns a new input stream to the content of this resource. The content
is represented on the resource through the osgi.content
capability. If more than one such capability is associated with the
resource, the first such capability is returned.