simscan - qmail virus and spam scanner

* Added quarantine thresshold. Only spam below quarantine limit will be
quarantined.
simcontrol now reads "spam_hits_quarantine"

Example:
simcontrol: "spam_hits=8.0, spam_hits_quarantine=12.0"
Spam above 8.0 gets rejected as usual.
Spam between 8.0 and 12.0 gets quarantined
Spam above 12.0 only gets rejected.

In the log:
<timestamp> simscan:[13030]:SPAM REJECT (9.60/4.00/8.0):9.4656s:Undelivered
Mail Returned to Sender:80.160.77.99::yhjenevt@domain.tld
<timestamp> simscan: Putting the message in quarantine:
/var/qmail/quarantine/msg.1202193987.799347.13033
<timestamp> simscan: Message recorded in quarantine successful


Quarantine is disabled if spam_hits_quarantine < 0 or not present.

* Added logline SPAM PASS. Mail below simscan's "spam_hits" but above
spamassassins "requred_hits" will be delivered. I added a log line with
SPAM PASS.

Example:
Spamassassin required_hits 4.0, simscan's spam_hits=7.5
Spam mail above 4.0 but below 7.5 will be let through but logged

<timestamp> simscan:[13880]:SPAM PASS (5.30/4.00/7.50):9.3834s:
Undeliverable Mail:64.71.40.36::_yeraktig@domain.tld


* Added the spamassassin requred hits to the logline

Example:
<timestamp> simscan:[13748]:CLEAN (-1.50/4.00/7.50):9.9144s:Not a spam
mail:10.0.0.4::email@domain.tld

* Bug fix in function is_spam()

elseif preventing the retrieval of SpamHits and ReqHits from spamassassin
header.