Update distro.conf

URL fix
Debian seems to have removed Netimage and provided some fixes

lib/distro.conf

@@ -63,8 +63,8 @@ wheezy-armel-netboot)
 wheezy-armhf-netboot)
 	#10-Oct-2013
 	#http://ftp.us.debian.org/debian/dists/wheezy/main/installer-armhf/
-	NETIMAGE="20130613+deb7u1"
+	NETIMAGE="20130613+deb7u1+b1"
-	TEST_MD5SUM="3220e4a90f1682f9b2a54c571e47ae0c"
+	TEST_MD5SUM="6a0197b064a9cdd23b25e93bc69e9221"
 	HTTP_IMAGE="http://ftp.debian.org/debian/dists"
 	BASE_IMAGE="mx5/netboot/efikamx"
 	UBOOTWRAPPER=1