Description of problem:
When installing mock on FC5 the development configs (actually the fedora-5*
configs, but that is bug 186478) do not reflect the new development layout. 

Version-Release number of selected component (if applicable):
mock-0.4-8.fc5

How reproducible:
Always

Steps to Reproduce:
build something in mock with a development configuration
  
Actual results:
404'ed, no repodata at that URL

Expected results:
Builds package.

Additional info:
The baseurl of the [core] section needs os/ appended to it.