[PATCH] Prevent false negative results of "make check" in Python tests

Hello,

discussed on IRC, the patch below changes the test harness to prevent
some false negatives when running the test suite. Specifically, if a
python test initialisation returns in such a way that the test runner
doesn't know how to handle the result, change to code to return a
non-zero exit code like and, subsequently, have "make check" fail
correctly. Reproducible by using Python < 2.5 or missing sqlite3 Python
bindings, exit triggered by
subversion/tests/cmdline/svntest/__init__.py. danielsh,breser hinted +1
for this on IRC.

[[[
Prevent false negative results of "make check" in Python tests

* build/run_tests.py
  (_run_py_test): exit non-zero like _run_c_test
]]]

With kind regards,
Andreas Stieger