Milter-greylist

Following patch contains changes below.

http://www.j10n.org/files/mgl-20070328-misc.patch

1. New "%%" syntax in fstring.

2. Clarified "%Xm" and "%Xh" semantics.

3. Fixed a memory leak at mlfi_eom.

4. Fixed the following bug:

% telnet mx.example.org 25
220 mx.example.org ESMTP
MAIL FROM:<black@...>
250 2.1.0 <black@...>... Sender ok
RCPT TO:<black@...>
551 5.7.1 Go away!
RCPT TO:<black@...>
250 2.1.0 <black@...>... Sender ok

As a side effect, the following problem in the comment will revive.

> a wrong X-Greylist header display
> if the {IP, sender e-mail} address was whitelisted and the
> last recipient was also whitelisted.

Anyway, X-Greylist header is just an estimate. No way to make
X-Greylist information accurate no matter how we implement it.
ACL's predictability is much more important than our useless header.