Fix dependencies on python-twisted
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This merge request is automatically copied from !227 (merged) orginally made by @ellert
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The Fedora packaging of python-twisted was changed a long time ago. The packages have had provides for the old package names for years, so the (build)requires in our specfile still worked, but they have now been dropped in the latest package update. The EPEL packages still use the old package names though, so it needs to be conditionalized.
Needs to be ported to ARC 5 svn to make the ARC 5 nighlies build on Fedora rawhide.
This is a resubmission of !215 (merged) after rebasing to current master.