use broadcast() instead of signal() when signaling the condition-variable Thread::RequestExitAndWait() is waiting for

we could have several thread waiting on the condition and they all need to wake-up.
also added a debug "mTid" field in the class, which contains the tid of the thread (as opposed to pthread_t), this
is useful when debugging under gdb for instance.
diff --git a/libs/utils/Threads.cpp b/libs/utils/Threads.cpp
index 6be372c..ec3db09 100644
--- a/libs/utils/Threads.cpp
+++ b/libs/utils/Threads.cpp
@@ -655,6 +655,11 @@
     wp<Thread> weak(strong);
     self->mHoldSelf.clear();
 
+#if HAVE_ANDROID_OS
+    // this is very useful for debugging with gdb
+    self->mTid = gettid();
+#endif
+
     bool first = true;
 
     do {
@@ -685,7 +690,7 @@
             self->mExitPending = true;
             self->mLock.lock();
             self->mRunning = false;
-            self->mThreadExitedCondition.signal();
+            self->mThreadExitedCondition.broadcast();
             self->mLock.unlock();
             break;
         }
@@ -693,7 +698,7 @@
         // Release our strong reference, to let a chance to the thread
         // to die a peaceful death.
         strong.clear();
-        // And immediately, reacquire a strong reference for the next loop
+        // And immediately, re-acquire a strong reference for the next loop
         strong = weak.promote();
     } while(strong != 0);