Description of problem:
When defining a custom installclass in the ks.cfg, the Kickstart method unlinks
the ks.cfg.new long before setInstallData (hence also readKickstart) is called.
This, of course, leads to a traceback when readKickstart tries to open the
long-gone file.

Version-Release number of selected component (if applicable):
anaconda-9.1.4.1-1.RHEL

How reproducible:
Always

Steps to Reproduce:
1. define a basic subclass of KickstartBase using %installclass in ks.cfg
2. try to use it
3.
  
Actual results:
Traceback - I can get the exact traceback on request, but all you need to do is
look at the code and you'll see it.

Expected results:
No traceback

Additional info:

FWIW, I wouldn't recommend counting on this functionality.  It's undocumented
from what I remember and very likely to go away (I know for a fact that it's
never tested :)