Java directors - more generic thread name setting

Activated if a user sets SWIG_JAVA_USE_THREAD_NAME.
Implementations provided for linux/android/macos/unix.
A user's implementation will be used if SWIG_JAVA_GET_THREAD_NAME is
defined. It must implement the function:
  namespace Swig {
    SWIGINTERN int GetThreadName(char *name, size_t len);
  }

Examples/test-suite/java/director_thread_runme.java

@@ -30,6 +30,12 @@ class director_thread_Derived extends Foo {
   }
 
   public void do_foo() {
+    // Not all operating systems can name threads, so only test on those that can
+    if (Foo.namedThread()) {
+      String threadName = Thread.currentThread().getName();
+      if (!threadName.equals("MyThreadName"))
+        throw new RuntimeException("Unexpected thread name: " + threadName);
+    }
     setVal(getVal() - 1);
   }
 }