FIX #1972 add regression test

sbt/src/sbt-test/package/mappings/build.sbt

@@ -0,0 +1,16 @@
+name := "Mappings Test"
+
+version := "0.2"
+
+mappings in (Compile, packageBin) ++= {
+  val test = file("test")
+  Seq(
+    test -> "test1",
+    test -> "test2"
+  )
+}
+
+lazy val unzipPackage = taskKey[Unit]("extract jar file")
+unzipPackage := {
+  IO.unzip((packageBin in Compile).value, target.value / "extracted")
+}

sbt/src/sbt-test/package/mappings/test

@@ -0,0 +1,3 @@
+> unzipPackage
+$ exists target/extracted/test2
+$ exists target/extracted/test1