Bug 981637:  Make overflow events fire correctly in UpdateOverflow codepath.  r=mats

I confirmed that the mochitest fails without the patch and passes with
it, both standalone and in the directory harness.
Bug 983558 - Test for return type when inlining ForkJoinGetSlice. (r=nmatsakis)
Bug 984063 - bail out of ion/bug977674.js when parallel isn't defined instead of making mozilla-aurora permaorange
Bug 981362 - Bail out of parallel/bug976889.js when parallel is not defined, rather than making aurora permaorange
Merge m-c to m-i