MINOR: applet: add an execution timeout

This patch only declares the execution timeout variable. The applet
must be respect or ignore it. For example an applet who doing some
network accesses and doesn't control its execution yime should use
this timeout.
diff --git a/include/types/applet.h b/include/types/applet.h
index 13817b2..799df91 100644
--- a/include/types/applet.h
+++ b/include/types/applet.h
@@ -40,6 +40,7 @@
 	                                     expect 1 if ok, 0 if an error occurs, -1 if miss data. */
 	void (*fct)(struct appctx *);      /* internal I/O handler, may never be NULL */
 	void (*release)(struct appctx *);  /* callback to release resources, may be NULL */
+	unsigned int timeout;              /* execution timeout. */
 };
 
 /* Context of a running applet. */