Still a work in progress as I haven't found how to avoid these deprecation message in layout-change and require test addons that are explicitely using old require paths to ensure that the mapping works...
I think I'm ok with landing this as is even though we'll have some warning in tests and figure how to remove them in the followup change.
Bug 841766 - We should warn users when magical require is used
Revert "Merge pull request #822 from ochameau/deprecate-mapping" for …
This reverts commit 66098bc, reversing
changes made to 2bdf0b9.
I had to revert this because it was unable to find the sdk/xul-app module and was throwing errors on all platforms.