[Yum] after "yum install fedora-release", can't update yum

[Robert P. J. Day]

  sorry for being such a pain, but in order to get the most recent
RPMs, i followed previous advice and ran

# yum install fedora-release

that seemed to work fine, /etc/redhat-release now shows
  
  Fedora Core release 0.95 (Severn)

but when i tried to update yum with 

# yum update yum

i got

Gathering header information file(s) from server(s)
Server: Red Hat Linux Null - i386 - Base
retrygrab() failed for:
  
http://mirror.dulug.duke.edu/pub/yum-repository/redhat/Null/i386/headers/header.info
  Executing failover method
failover: out of servers to try
Error getting file 
http://mirror.dulug.duke.edu/pub/yum-repository/redhat/Null/i386/headers/header.info
[Errno 4] IOError: HTTP Error 404: Not Found

  apparently, the $releasever value in /etc/yum.conf is being replaced by 
"Null".  what have i pooched here?

rday