OpenStack components, including Savanna, are moving to pbr. Savanna is going to require pbr>=0.5.21. Please upgrade F19+ to 0.5.21+.
Rawhide has already pbr-0.5.21. IMHO for f19 it's forbidden by policy: http://fedoraproject.org/wiki/Updates_Policy#Stable_Releases especially since pbr was really good in introducing new features or to change them even in minor releases. Do you really need it, esp. as runtime requirement? It is clearly possible to build in rawhide, like we do for all other OpenStack components.
I can't speak to the stability / instability of pbr and its backward compatibility. I would hope it has good compatibility, but that may not be the case. FYI - https://github.com/openstack-dev/pbr/compare/0.5.19...0.5.21 I'm planning to try 0.5.19 w/ a sed -i edit when the pbr changes are committed to Savanna. Feel free to close this out, but I may re-open it if I can't workaround in the spec.