Give the sidebar iframe a name

This simplifies the tests a little bit, maybe it will be more
robust???

Also seems like a useful thing to do anyway.

h/js/host.coffee

@@ -19,6 +19,7 @@ class Annotator.Host extends Annotator.Guest
       hostOrigin ?= window.location.protocol + "//" + window.location.host
 
     app = $('<iframe></iframe>')
+    .attr('name', 'hyp_sidebar_frame')
     .attr('seamless', '')
     .attr('src', "#{options.app}#/?xdm=#{encodeURIComponent(hostOrigin)}")