Add virtual ~Thread() to avoid warnings.

git-svn-id: https://google-glog.googlecode.com/svn/trunk@58 eb4d4688-79bd-11dd-afb4-1d65580434c0

src/googletest.h

@@ -525,6 +525,8 @@ struct FlagSaver {
 
 class Thread {
  public:
+  virtual ~Thread() {}
+
   void SetJoinable(bool joinable) {}
 #if defined(HAVE_PTHREAD)
   void Start() {