[rqlrewrite] fix rqlrewrite unpredictability vs relation sharing. Closes #3036144 The relations index used to determine if relation may be shared only considered a single relation node per relation type. So when the same relation type occurs several time, dict order give unpredictable result. We shall properly consider all relations instead. Tentative test case included (but bug reproduction is by definition unpredictable...)

fontcolor = 'black'
bgcolor = '#FFFFFF'
stylesheets = sheet['stylesheets'] + ['%s/mycube.css' % datadir_url]