Bug 1015482 part 1: Add 'min-width: 0' to some reftest files that have flex items with intentionally-overflowing contents. r=mats
Bug 1015482 part 2: Adjust sizes in some flexbox reftests so that min-width:auto won't affect their rendering. r=mats
Bug 1015563: Soften flexbox assertion that can fail from integer overflow. r=mats