howto build a package against a recently built other package

[David Timms <dtimms iinet net au>]

Hi. x11vnc build for EL6 now succeeds (after excluding ppc64 javaviewer
package).
http://koji.fedoraproject.org/koji/taskinfo?taskID=2728535

This means I think I need to rebuild my dependent pyvnc2swf package
against it.

Having not needed to do this before, I tried:
$ cd pyvnc2swf/el6
$ fedpkg chain-build x11vnc
Could not initiate build: Packages in destination tag
dist-6E-epel-testing-candidate are not inherited bybuild tag
dist-6E-epel-build

I guess I don't understand the chain-build, nor the split indicated
above. How does it work ? What is the appropriate command then ?