[css-line-grid] add issue for box-snap:auto value
[css3-gcpm] move alternative running element syntax into issue; add issue about footnotes in multicol
merge
[css-flexbox] Fix dholbert's issue with items that'll get clamped past their base size causing bad free space calculations.

--HG--
extra : rebase_source : 5c8149f49a7c1a90f7a9e716daddfdd0c5239fef