* tests/*.py: use the DSN constructed in tests/__init__.py.
* tests/__init__.py: allow setting the host, port and user for the
DSN used by the tests through the environment.
patch from ticket #209 to check return value from
PyObject_AsCharBuffer(). This fixes the segfault.
(binary_quote): switch from PyObject_AsCharBuffer() to
PyObject_AsReadBuffer() to support buffer objects that don't
implement the bf_getcharbuf protocol.
* tests/types_basic.py (TypesBasicTests.testBinary): Test round
tripping of bytea buffers. Currently segfaults.
