Fix some bugs found by static analysis

I didn't do all of them. Here are the others. 

```
--------------------------------
File       : lib/phpqrcode/qrtools.php:75
Reason     : UseUndeclaredVariable
Snippet    : QRtools::$frames
Line       : self::$frames = array();
--------------------------------
File       : classes/pref/feeds.php:790
Reason     : UseUndeclaredVariable
Snippet    : $title
Line       : name=\"title\" value=\"$title\">";
--------------------------------
File       : classes/pref/feeds.php:801
Reason     : UseUndeclaredVariable
Snippet    : $feed_url
Line       : name=\"feed_url\" value=\"$feed_url\">";
--------------------------------
File       : classes/pref/feeds.php:813
Reason     : UseUndeclaredVariable
Snippet    : $cat_id
Line       : print_feed_cat_select("cat_id", $cat_id,
--------------------------------
File       : classes/pref/feeds.php:827
Reason     : UseUndeclaredVariable
Snippet    : $update_interval
Line       : print_select_hash("update_interval", $update_interval, $update_intervals,
--------------------------------
File       : classes/pref/feeds.php:840
Reason     : UseUndeclaredVariable
Snippet    : $purge_interval
Line       : print_select_hash("purge_interval", $purge_interval, $purge_intervals,
--------------------------------
File       : classes/pref/feeds.php:852
Reason     : UseUndeclaredVariable
Snippet    : $auth_login
Line       : name=\"auth_login\" value=\"$auth_login\">";
--------------------------------
File       : classes/pref/feeds.php:858
Reason     : UseUndeclaredVariable
Snippet    : $auth_pass
Line       : value=\"$auth_pass\">";
--------------------------------
File       : lib/phpqrcode/phpqrcode.php:208
Reason     : UseUndeclaredVariable
Snippet    : QRtools::$frames
Line       : self::$frames = array();
--------------------------------
File       : lib/phpqrcode/phpqrcode.php:2126
Reason     : UseUndeclaredVariable
Snippet    : $run
Line       : return $run;
--------------------------------
File       : lib/pubsubhubbub/subscriber.php:47
Reason     : TooFewArgument
Snippet    : $this->http($url)
Line       : $response = $this->http($url);
--------------------------------
```