Timer: new implementation (merge finished, tests failing)

src/execplugin/execplugin.h

@@ -46,7 +46,7 @@ typedef struct ExecpBackend {
     Background *bg;
 
     // Backend state:
-    timeout *timer;
+    Timer timer;
     int child_pipe_stdout;
     int child_pipe_stderr;
     pid_t child;