Adding Filter.php

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The class Fz_Filter implements a general purpose filter for FileZ. Filters have
a syntax very similar to their counterparts in LDAP. The main difference is
that expressions are PERL non-anchored, case insensitive regular expressions
whereas LDAP uses unix shell-like wildcards.

The primary goal for filters is to grant or deny access to authenticated
users if a set of criteria is satisfied of not. For example, consider a FileZ
site which uses its own authentication handler MyAuth and requires that users
can only deposit files from hosts satisfying one or both of these conditions :
the IP address belong to the network 192.168.1.0/24 or the hostname contains
the string mydomain. Add the following line in config/filez.ini:
	[auth_options]
	filter = "(|(REMOTE_ADDR=^192\.168\.1\.\d+)(HTTP_HOST=mydomain))"

Add the following code in lib/Fz/Controller/Security/MyAuth.php
	protected function _doSecure() {
	    ...
	    $filter = new Fz_Filter($this->getOption ("filter", null));
        if (! $filter->applyTo($_SERVER)) {
            throw new Exception("Sorry, you are not allowed to use this server");
        }
		...
    }