service: kill stubborn services, wait before restart

Add support for registering callbacks to be called after a given
timeout.

Use this to implement forceful termination of services that refuse to
terminate upon receiving a SIGTERM. If the service PID is not collected
within 3 seconds, send a SIGKILL to it.

Also, rework restarting of crashing services. When a service crashes for
the first time, try to restart it immediately. If it crashes again, wait
a few seconds before trying again. Just as before, if it continues to
crash, block the service.

finit.h

@@ -34,6 +34,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <lite/lite.h>
+#include <uev/uev.h>
 
 #define CMD_SIZE                256
 #define LINE_SIZE               1024
@@ -90,6 +91,8 @@ extern char  *hostname;
 extern char  *username;
 extern char  *runparts;
 extern char  *console;
+extern uev_ctx_t *ctx;
+
 extern char  *__progname;
 
 #endif /* FINIT_H_ */