java usages highlighting: add an additional test for multiple jdk configuration

java/java-tests/testData/codeInsight/multipleJdks/java7/p/List7.java

@@ -0,0 +1,11 @@
+package p;
+
+import java.util.AbstractList;
+import java.util.Collection;
+
+public abstract class List7 extends AbstractList<String> {
+  @Override
+  public boolean addAll(Collection<? extends String> c) {
+    return true;
+  }
+}