Add a pending test-case for showing circular api structures.

This test should pass because `ShowAPI` skips inherited members but
due to sbt/sbt#676 it fails with StackOverflowError.

This makes it a decent test-case for both showing circular api structures
and for the aforementioned bug itself.

sbt/src/sbt-test/api/show-circular-structure/build.sbt

@@ -0,0 +1,12 @@
+logLevel := Level.Debug
+
+incOptions ~= { _.copy(apiDebug = true) }
+
+TaskKey[Unit]("show-apis") <<= (compile in Compile, scalaSource in Compile, javaSource in Compile) map { (a: sbt.inc.Analysis, scalaSrc: java.io.File, javaSrc: java.io.File) =>
+  val aApi = a.apis.internalAPI(scalaSrc / "A.scala").api
+  val jApi = a.apis.internalAPI(javaSrc / "test/J.java").api
+  import xsbt.api.DefaultShowAPI
+  import DefaultShowAPI._
+  DefaultShowAPI.showSource.show(aApi)
+  DefaultShowAPI.showSource.show(jApi)
+}

sbt/src/sbt-test/api/show-circular-structure/pending

@@ -0,0 +1,4 @@
+# test case for http://github.com/sbt/sbt/issues/676
+> compile
+# fails with StackOverflowException
+> show-apis

sbt/src/sbt-test/api/show-circular-structure/src/main/java/test/J.java

@@ -0,0 +1,6 @@
+package test;
+
+public class J {
+  public static final class J2 extends J { }
+  public static final class J3 extends J { }
+}

sbt/src/sbt-test/api/show-circular-structure/src/main/scala/A.scala

@@ -0,0 +1,6 @@
+package test
+
+class A {
+	class B extends A
+	class C extends A
+}