Macrotracker support

Hi !

> MacroTracker is a compiler plugin for scalac 2.11.0. Its job is to register all the symbols that are touched during the expansion of a macro, and attach them to the expanded macro. Using this information, we can deduct the dependencies between the expanded macro and everything that has been involved in its expansion. 

(From [this thread in sbt-dev](https://groups.google.com/forum/#!topic/sbt-dev/clIbzCp9VX8))

MacroTracker helps to track the dependencies that are introduced using the reflection API. Whenever a symbol is accessed using the reflection API, MacroTracker registers it and finally attaches all the touched symbols to the expanded macro.

It can help greatly in cases such as the ones that are exposed in the [accompanied scripted test](https://github.com/Duhemm/sbt/tree/macrotracker-support/sbt/src/sbt-test/source-dependencies/macro-macrotracker).

MacroTracker can be found here : [scalamacros/macrotracker](https://github.com/scalamacros/macrotracker).