Add callback hack to find out when to reload system properties.

Every IBinder object can accept a new transaction to tell it that
it might want to reload system properties, and in the process
anyone can register a callback to be executed when this happens.

Use this to reload the trace property.

This is very much ONLY for debugging.

Change-Id: I55c67c46f8f3fa9073bef0dfaab4577ed1d47eb4
diff --git a/include/binder/IBinder.h b/include/binder/IBinder.h
index 81b56c2..8b84951 100644
--- a/include/binder/IBinder.h
+++ b/include/binder/IBinder.h
@@ -51,6 +51,7 @@
         PING_TRANSACTION        = B_PACK_CHARS('_','P','N','G'),
         DUMP_TRANSACTION        = B_PACK_CHARS('_','D','M','P'),
         INTERFACE_TRANSACTION   = B_PACK_CHARS('_', 'N', 'T', 'F'),
+        SYSPROPS_TRANSACTION    = B_PACK_CHARS('_', 'S', 'P', 'R'),
 
         // Corresponds to TF_ONE_WAY -- an asynchronous call.
         FLAG_ONEWAY             = 0x00000001