move all $fetch globals to UrlHelper

backend.php

classes/feeds.php

classes/rssutils.php

classes/urlhelper.php

include/functions.php

plugins/af_comics/filters/af_comics_cad.php

plugins/af_comics/filters/af_comics_darklegacy.php

plugins/af_comics/filters/af_comics_dilbert.php

plugins/af_comics/filters/af_comics_whomp.php

plugins/af_proxy_http/init.php

plugins/af_readability/init.php

plugins/af_redditimgur/init.php