Generic virus plugin support

[John Peacock]

Now that I have three different AV packages installed, I want to find a 
way to run all three in a random fashion (rather than just one after 
another).  I can't think of a way to use the plugin wrapping API, since 
I want to have a single place where I check to see if the message is 
multi-part and skip all.  I also want to assign percentages to each 
scanner so that one might run more often than another.

I wonder if this wouldn't be best handled by making the config file YAML 
aware, so I could have something like this:

antivirus_wrapper:
  - scanner: exe_filter
    freq: 1.0
  - scanner: uvscan
    args: "deny_viruses yes"
    freq: 0.35
  - scanner: bitdefender
    args: "deny_viruses yes"
    freq: 0.35
  - scanner: clamav
    args: "clamscan_path=/usr/local/bin/clamdscan action=reject"
    freq: 0.55
where 'antivirus_wrapper' is given the rest of the lines and winds up 
registering each of the other plugins to a custom event.  Then some sort 
of fancy math can happen where the three later plugins are randomly 
selected (sometimes more than one runs but never all three), and the 
exe_filter always runs (and if the message isn't multipart, they are all 
skipped).

Thoughts?
John