init: create android::init:: namespace

With some small fixups along the way

Test: Boot bullhead
Test: init unit tests
Change-Id: I7beaa473cfa9397f845f810557d1631b4a462d6a
diff --git a/init/signal_handler.h b/init/signal_handler.h
index 449b4af..f7881ab 100644
--- a/init/signal_handler.h
+++ b/init/signal_handler.h
@@ -17,6 +17,12 @@
 #ifndef _INIT_SIGNAL_HANDLER_H_
 #define _INIT_SIGNAL_HANDLER_H_
 
+namespace android {
+namespace init {
+
 void signal_handler_init(void);
 
+}  // namespace init
+}  // namespace android
+
 #endif