SourceMap and Simple Strategies have varying support for aboslute paths

[stefanpenner]

It appears the during SourceMap concat, we accidentally support absolute paths, but in Simple we do not. We should actually never support absolute paths, and that was merely a mistake.

People run into this, in ember via app.import(someAbsolutePath). And it leads to sadness and confusion, as often they run sourceMaps in dev, but not prod. Resulting in dev including the file and prod not. This sucks.

Two options:

a) We drop support for absolute paths and the rollout plan would be something like:

1. we warn when we see an absolute path today
2. we do a major version that changes this warn to an assert
3. profit

b) We add support uniformly for absolute paths.