obfuscate urls and fix note about them

Originally committed as revision 10124 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/issue_tracker.txt

@@ -13,11 +13,11 @@ a mail for every change to every issue. Replies to such mails will also
 properly be added to the respective issue.
 (the above does all work already after light testing)
 The subscription URL for the ffmpeg-issues list is:
-http://live.polito.it/mailman/listinfo/ffmpeg-issues
+http://live.polito/mailman/listinfo/ffmpeg-issues
 The URL of the webinterface of the tracker is:
 http(s)://roundup.mplayerhq/roundup/ffmpeg/
-Note the use the URLs above you must append top level domain of
-hungary to the tracker, and italy to the mailinglist
+Note the URLs in this document are obfuscated, you must append top level
+domain of hungary to the tracker, and italy to the mailinglist.
 
 Email Interface:
 ----------------