image download +b1 has been changed to +b2 for wheezy-armhf

When running the mk_mmc.sh script for Debian wheezy-armhf the
following error results.

jeri@hudson:~/beagleboard/netinstall$ sudo ./mk_mmc.sh --mmc /dev/sdb --dtb am335x-boneblack --distro wheezy-armhf

...

Downloading NetInstall Image
-----------------------------
--2014-02-08 10:09:24--  http://ftp.debian.org/debian/dists/wheezy/main/installer-armhf/20130613+deb7u1+b1/images/mx5/netboot/efikamx/uInitrd
Resolving ftp.debian.org (ftp.debian.org)... 130.89.148.12, 2001:610:1908:b000::148:12
Connecting to ftp.debian.org (ftp.debian.org)|130.89.148.12|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2014-02-08 10:09:24 ERROR 404: Not Found.

jeri@hudson:~/beagleboard/netinstall$

It appears that the url has changed from +b1 to +b2

old url, broken (+b1)
http://ftp.debian.org/debian/dists/wheezy/main/installer-armhf/20130613+deb7u1+b1/images/mx5/netboot/efikamx/uInitrd

new url, OK (+b2)
http://ftp.debian.org/debian/dists/wheezy/main/installer-armhf/20130613+deb7u1+b2/images/mx5/netboot/efikamx/