Wordpress debug error fixs

Some fixes to remove errors being displayed by Wordpress when WP_DEBUG mode is on.

Tested and working with Wordpress 3.6

Stacktrace of errors from login:

```
Notice: Undefined index: step in /vagrant/www/public/wp-content/plugins/authy-two-factor-authentication/authy.php on line 1244

Call Stack:
    0.0067    1134960   1. {main}() /vagrant/www/public/wp-login.php:0
    0.4453   32200096   2. wp_signon() /vagrant/www/public/wp-login.php:622
    0.4454   32202952   3. wp_authenticate() /vagrant/www/public/wp-includes/user.php:53
    0.4455   32203664   4. apply_filters() /vagrant/www/public/wp-includes/pluggable.php:472
    0.4455   32206448   5. call_user_func_array() /vagrant/www/public/wp-includes/plugin.php:173
    0.4455   32206520   6. Authy-&gt;authenticate_user() /vagrant/www/public/wp-includes/plugin.php:0

Notice: Undefined index: authy_signature in /vagrant/www/public/wp-content/plugins/authy-two-factor-authentication/authy.php on line 1245

Call Stack:
    0.0067    1134960   1. {main}() /vagrant/www/public/wp-login.php:0
    0.4453   32200096   2. wp_signon() /vagrant/www/public/wp-login.php:622
    0.4454   32202952   3. wp_authenticate() /vagrant/www/public/wp-includes/user.php:53
    0.4455   32203664   4. apply_filters() /vagrant/www/public/wp-includes/pluggable.php:472
    0.4455   32206448   5. call_user_func_array() /vagrant/www/public/wp-includes/plugin.php:173
    0.4455   32206520   6. Authy-&gt;authenticate_user() /vagrant/www/public/wp-includes/plugin.php:0

Notice: Undefined index: authy_user in /vagrant/www/public/wp-content/plugins/authy-two-factor-authentication/authy.php on line 1246

Call Stack:
    0.0067    1134960   1. {main}() /vagrant/www/public/wp-login.php:0
    0.4453   32200096   2. wp_signon() /vagrant/www/public/wp-login.php:622
    0.4454   32202952   3. wp_authenticate() /vagrant/www/public/wp-includes/user.php:53
    0.4455   32203664   4. apply_filters() /vagrant/www/public/wp-includes/pluggable.php:472
    0.4455   32206448   5. call_user_func_array() /vagrant/www/public/wp-includes/plugin.php:173
    0.4455   32206520   6. Authy-&gt;authenticate_user() /vagrant/www/public/wp-includes/plugin.php:0
    
Notice: Undefined variable: errors in /vagrant/www/public/wp-content/plugins/authy-two-factor-authentication/authy.php on line 1040

Call Stack:
    0.0068    1140200   1. {main}() /vagrant/www/public/wp-login.php:0
    1.5317   32308104   2. wp_signon() /vagrant/www/public/wp-login.php:622
    1.5318   32311080   3. wp_authenticate() /vagrant/www/public/wp-includes/user.php:53
    1.5319   32311584   4. apply_filters() /vagrant/www/public/wp-includes/pluggable.php:472
    1.5319   32314376   5. call_user_func_array() /vagrant/www/public/wp-includes/plugin.php:173
    1.5319   32314448   6. Authy-&gt;authenticate_user() /vagrant/www/public/wp-includes/plugin.php:0
    1.5319   32314688   7. Authy-&gt;verify_password_and_redirect() /vagrant/www/public/wp-content/plugins/authy-two-factor-authentication/authy.php:1249
    4.6478   32440336   8. Authy-&gt;render_authy_token_page() /vagrant/www/public/wp-content/plugins/authy-two-factor-authentication/authy.php:1095
      
Notice: Undefined index: rememberme in /vagrant/www/public/wp-content/plugins/authy-two-factor-authentication/authy.php on line 1262

Call Stack:
    0.0022    1139688   1. {main}() /vagrant/www/public/wp-login.php:0
    0.2455   32209136   2. wp_signon() /vagrant/www/public/wp-login.php:622
    0.2456   32211992   3. wp_authenticate() /vagrant/www/public/wp-includes/user.php:53
    0.2457   32212704   4. apply_filters() /vagrant/www/public/wp-includes/pluggable.php:472
    0.2457   32215488   5. call_user_func_array() /vagrant/www/public/wp-includes/plugin.php:173
    0.2457   32215560   6. Authy-&gt;authenticate_user() /vagrant/www/public/wp-includes/plugin.php:0
```