Merge branch 'margo-additions' into 'master'
Margo additions I beefed up the margo-related part of ssg, including a "barrier" call (with naive implementation). I also tweaked the example programs. @ssnyder, mind taking a quick look at the API and see if anything's goofy? Also, I changed the name of ssg to "Simple Static Group" here - it will go into master one way or another. See merge request !1