All 'addon' subprojects now have their sources aggregated into the addons subproject. This is done via a source copy (so that sbt will only rebuild sources that actually changed). To prevent caching issues the addons/src directory is CLEARED and then refilled every time addons is compiled. Thus, it is CRUCIAL NO SOURCES ARE MANUALLY ADDED TO addons/src AS THEY WILL BE WIPED BY addons/prepare. Due to sbt source caching, sbt will still be able to tell which sources have changed. (Strangely, sbt would not cache sources in extra unmanaged source directories and thus would always recompile them.) Also, cleaned up project/build.scala a bit to remove some warnings: Added import scala.language/postFixOps (so make! at the bottom no longer errors) and .toURI.toURL (as straight .toURL has been deprecated by the java standard library).
