Improvements for automated port lint

[Ryan Schmidt]

Thanks to William Siegrist for setting up the automated port lint and  
email following each commit! Now here's some thoughts about some  
problems and how they could be dealt with.

* I'm worried what will happen when someone does a batch cleanup  
operation affecting dozens or hundreds of portfiles in a single  
commit. (We've had this situation in r33441, r30218, r28561, r22478,  
r19376, etc.) I don't want this to fire off dozens or hundreds of  
lint emails. A thought here is that if a single commit affects, say,  
more than 5 portfiles, no lint report is run and no emails are sent.  
Or, just one email could be sent to the committer, letting them know  
why lint was not run.

* The subject line of the lint emails reads "[MacPorts Lint] Portfile  
Lint Errors for: <port>". Not all information returned by lint is an  
error though; some of it is just warnings. There's also a lot of  
words up front there in the subject that I don't need. I would change  
the subject to "[<rev>] <port> lint report"

* Possibly obsoleting both of the above observations, what would  
people think about appending the port lint report to the diff email  
that's already generated and sent to macports-changes? I'm not sure  
if this is the best idea, or even possible with the diff email script  
we use, but the idea occurred to me so I thought I'd see what others  
think.