Summary: Fixes T6011. See that task for discussion. We can detect when `memory_limit` will be the limiting factor for drag-and-drop uploads and warn administrators about it. Test Plan: Fiddled configuration values and hit, then resolved, the issue. Reviewers: btrahan Reviewed By: btrahan Subscribers: epriestley Maniphest Tasks: T6011 Differential Revision: https://secure.phabricator.com/D10413