This is just a tracker bug for an upstream issue.
this "fixes" compilation of the module by not using the problematic finally block
Got a fix from upstream: https://mail.python.org/pipermail/cython-devel/2015-August/004492.html.
Applied as a patch to the rpmbuild in r10337. I think I will keep this 0.23-2 in beta only and post 0.23.1 to stable when it is released.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/947