MEDIUM: Make 'resolution_pool_size' directive fatal

This directive never appeared in a stable release and instead was
introduced and deprecated within 1.8-dev. While it technically could
be outright removed we detect it and error out for good measure.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 8aa9f2c..7543cc3 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -12759,11 +12759,6 @@
 
   Default value is 10s for "valid", 0s for "obsolete" and 30s for others.
 
-resolution_pool_size <nb>  (deprecated)
-  Defines the number of resolutions available in the pool for this resolvers.
-  If not defines, it defaults to 64. If your configuration requires more than
-  <nb>, then HAProxy will return an error when parsing the configuration.
-
 resolve_retries <nb>
   Defines the number <nb> of queries to send to resolve a server name before
   giving up.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index ab5a2eb..a16628a 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -1250,9 +1250,9 @@
 		curr_resolvers->accepted_payload_size = i;
 	}
 	else if (strcmp(args[0], "resolution_pool_size") == 0) {
-		ha_warning("parsing [%s:%d] : '%s' directive is now deprecated and ignored.\n",
+		ha_alert("parsing [%s:%d] : '%s' directive is not supported anymore (it never appeared in a stable release).\n",
 			   file, linenum, args[0]);
-		err_code |= ERR_WARN;
+		err_code |= ERR_ALERT | ERR_FATAL;
 		goto out;
 	}
 	else if (strcmp(args[0], "resolve_retries") == 0) {