MDL-5598 - Custom feed titles on RSS block did not allow spaces or other

useful characters ;)

merged from MOODLE_19_STABLE

blocks/rss_client/block_rss_client_action.php

@@ -47,7 +47,7 @@
 $rssid          = optional_param('rssid', NULL, PARAM_INT);
 $id             = optional_param('id', SITEID, PARAM_INT);
 //$url            = clean_param($url, PARAM_URL);
-$preferredtitle = optional_param('preferredtitle', '', PARAM_ALPHA);
+$preferredtitle = optional_param('preferredtitle', '', PARAM_TEXT);
 $shared         = optional_param('shared', 0, PARAM_INT);