[CentOS-mirror] mirror.umoss.org -> mirror.umd.edu

Our mirror has moved from mirror.umoss.org to mirror.umd.edu. We are
now carrying the entire CentOS tree, and we have added FTP access.

Our addresses are now:

http://mirror.umd.edu/centos/
rsync://mirror.umd.edu/centos/
ftp://mirror.umd.edu/centos/