BUG/MINOR: log: fix log-format parsing errors

Some errors were still reported as log-format instead of their respective
contexts (acl, request header, stick, ...). This is harmless and does not
require any backport.
diff --git a/src/log.c b/src/log.c
index a1e5db9..dd65e26 100644
--- a/src/log.c
+++ b/src/log.c
@@ -166,14 +166,22 @@
  */
 static inline const char *fmt_directive(const struct proxy *curproxy)
 {
-	if (curproxy->conf.args.ctx == ARGC_UIF)
+	switch (curproxy->conf.args.ctx) {
+	case ARGC_UIF:
 		return "unique-id-format";
-	else if (curproxy->conf.args.ctx == ARGC_HRQ)
+	case ARGC_HRQ:
 		return "http-request";
-	else if (curproxy->conf.args.ctx == ARGC_HRS)
+	case ARGC_HRS:
 		return "http-response";
-	else
+	case ARGC_STK:
+		return "stick";
+	case ARGC_TRK:
+		return "track-sc"; break;
+	case ARGC_ACL:
+		return "acl"; break;
+	default:
 		return "log-format";
+	}
 }
 
 /*
@@ -277,7 +285,7 @@
 					        logformat_keywords[j].name, fmt_directive(curproxy), logformat_keywords[j].replace_by);
 				return 0;
 			} else {
-				Warning("parsing [%s:%d] : '%s' variable name '%s' is reserved for HTTP mode\n",
+				Warning("parsing [%s:%d] : '%s' : format variable '%s' is reserved for HTTP mode\n",
 				        curproxy->conf.args.file, curproxy->conf.args.line, fmt_directive(curproxy),
 				        logformat_keywords[j].name);
 				return -1;
@@ -287,7 +295,7 @@
 
 	j = var[var_len];
 	var[var_len] = 0;
-	Warning("parsing [%s:%d] : no such variable name '%s' in '%s'\n",
+	Warning("parsing [%s:%d] : no such format variable '%s' in '%s'\n",
 	        curproxy->conf.args.file, curproxy->conf.args.line, var, fmt_directive(curproxy));
 	var[var_len] = j;
 	return -1;