I tried running release 1.5 on CentOS 6.4 with the version of Mercurial and Python that comes with the OS and the tests failed with both SWIG and Subvertpy. Here's the output of hg version --svn with Subvertpy:
With Subvertpy: Mercurial Distributed SCM (version 1.4)
hgsubversion: 77b22e5b4ea6 Subversion: 1.6.11 bindings: Subvertpy 0.8.10
With SWIG it's identical but just says SWIG for the bindings.
Is there anything that I can do to help further diagnose the issue?