Log line-at-a-time to work around Android logging lossage.

Also deduplicate the two copies of gettid, and switch image_test over
to using SignalCatcher's SIGQUIT dumping rather than rolling its own
subset.

Change-Id: I8b70aaa3a3b9258c8258728c6a66e5dc4fa6399e
diff --git a/src/signal_catcher.h b/src/signal_catcher.h
index 1c08542..a31b9f1 100644
--- a/src/signal_catcher.h
+++ b/src/signal_catcher.h
@@ -34,9 +34,10 @@
   SignalCatcher();
   ~SignalCatcher();
 
+  static void HandleSigQuit();
+
  private:
   static void* Run(void* arg);
-  static void HandleSigQuit();
   static void HandleSigUsr1();
 
   static bool halt_;