[entity] more tweaks for entity attribute cache handling on cw_set/cw_create to fix test regression * when an attribute is listed in dont-cache-attrs, purge any previous value * test value is actually modified in EditedEntity.__setitem__ before adding attribute to dont-cache-attrs

bgcolor = '#000000'
stylesheets = ['%s/cubicweb.css' % datadir_url]
logo = '%s/logo.png' % datadir_url
lazy = lazystr('%(bgcolor)s')