Sentinel: announce ip/port changes + rewrite.

The original implementation was modified in order to allow to
selectively announce a different IP or port, and to rewrite the two
options in the config file after a rewrite.

src/config.c

@@ -1427,7 +1427,7 @@ void rewriteConfigStringOption(struct rewriteConfigState *state, char *option, c
         return;
     }
 
-    /* Compare the strings as sds strings to have a binary safe comparison. */
+    /* Set force to zero if the value is set to its default. */
     if (defvalue && strcmp(value,defvalue) == 0) force = 0;
 
     line = sdsnew(option);