MINOR: proxy: add a new capability PR_CAP_DEF

In order to more easily distinguish a default proxy from a standard one,
let's introduce a new capability PR_CAP_DEF.
diff --git a/src/cfgparse-listen.c b/src/cfgparse-listen.c
index ffe7931..1760259 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -192,10 +192,12 @@
 		rc = PR_CAP_FE;
 	else if (strcmp(args[0], "backend") == 0)
 		rc = PR_CAP_BE;
+	else if (strcmp(args[0], "defaults") == 0)
+		rc = PR_CAP_DEF;
 	else
 		rc = PR_CAP_NONE;
 
-	if (rc != PR_CAP_NONE) {  /* new proxy */
+	if (rc & PR_CAP_LISTEN) {  /* new proxy */
 		if (!*args[1]) {
 			ha_alert("parsing [%s:%d] : '%s' expects an <id> argument\n",
 				 file, linenum, args[0]);
@@ -257,7 +259,7 @@
 		curproxy = &defproxy;
 		curproxy->conf.args.file = curproxy->conf.file = strdup(file);
 		curproxy->conf.args.line = curproxy->conf.line = linenum;
-		defproxy.cap = PR_CAP_LISTEN; /* all caps for now */
+		defproxy.cap = PR_CAP_DEF | PR_CAP_LISTEN; /* all caps for now */
 		goto out;
 	}
 	else if (curproxy == NULL) {