Question about DMD's Travis CI

[Michael V. Franklin via Digitalmars-d]

I've been battling DMD's Travis CI for the past couple of weeks 
with a few of my pull requests.  It often fails for various 
reasons that have nothing to do with my PRs (e.g. "The job 
exceeded the maximum time limit for jobs, and has been 
terminated.")  It's also takes almost half a day to complete.

What is the purpose of Travis CI?  What is it testing for that 
the much more reliable AutoTester isn't already testing for?  Can 
anything be done to make it more reliable and efficient?

Thanks,
Mike