Fixes multiple literate coffeescript files with `sourceMap: true`

Fixing task to recognize .litcoffee and .coffee.md when `sourceMap: true`.

Originally, multiple `.litcoffee` and `.coffee.md` files where compiling into the default `fileExt: '.src.coffee'`.  Now when there are multiple literate coffescript files and  the "joinExt" src.litcoffee" or ".coffee.md" is provided, the tasks recognize the concatenated script as literate coffee script.