conf: convert zone name to lower-case

fixes #207

src/knot/conf/cf-parse.y

@@ -23,6 +23,7 @@
 %{
 
 #include <config.h>
+#include <ctype.h>
 #include <limits.h>
 #include <stdio.h>
 #include <string.h>
@@ -347,6 +348,11 @@ static void conf_zone_start(void *scanner, char *name) {
 		this_zone->name = name; /* Already FQDN */
 	}
 
+	// Convert zone name to lower-case.
+	for (size_t i = 0; this_zone->name[i]; i++) {
+		this_zone->name[i] = tolower(this_zone->name[i]);
+	}
+
 	// DNSSEC configuration
 	this_zone->dnssec_enable = -1;