[dmd-internals] pull queue management

[Brad Roberts via dmd-internals]

Ok, everyone knows the pull queues are huge and that a goal of clearing 
them is long term at best.  I have a much more targeted suggested goal:  
Keep the stable pull queue empty.  There's currently 11 pull requests.  
There's really no reason for this subset to linger.  Either they're good 
and low risk fixes for issues or they should be done on master.

     https://auto-tester.puremagic.com/pulls.ghtml?projectid=14
     Or a github search with the filter: base:stable
https://github.com/dlang/dmd/pulls?utf8=%E2%9C%93&q=is%3Apr%20is%3Aopen%20base%3Astable

A quick bit of focused effort to handle the existing queue then a daily 
job to send an email about the existence of anything older than a day?  
Or maybe anything at all.