Adjacent TCP and UDP ports must not be joined.
Support for setting log severity.

Logging is changed by a combination of attributes at rules and
devices.

Define one or more lines "log:<tag> = <severity>" at devices, where
logging should be enabled or changed.
- <tag> is some valid identifier.
- <severity> is one of
  alerts|critical|debugging|disable|emergencies|
  errors|informational|notifications|warnings

Define attribute "log = <tag1>, ...;" at each rule that needs changed logging.
A rule with logging for <tag1> is logged at each device, where a
matching "log:<tag1>" is defined.

Severity names correspond to well known UNIX log severities.
'disable' disables logging at devices of type ASA and PIX.

This fixes #9.