Allow login to any account by using any administrator's password
There are none. If the plugin is active, then you can log in by entering any valid username together with the password of any user with administrator privileges.
Please either send a patch, or make a suitable donation on my donation page, and I will be glad to help. Otherwise, this plugin does all I wanted it to do and I've not got time to develop it further.
That's nothing to do with this plugin. This plugin gives you an extra way to validate a login (by knowing an administrator's password), but does nothing else to remove or lock-down any other authentication settings which you have.
Glad to hear that! You are looking for WordShell, http://wordshell.net.