* 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.
requiring it.
Added a connection flag to store whether E''-style quoting is required: this
avoids repeated PQparameterStatus() calls.
Added a test case to verify correct behavior on strings, unicode and binary
data. Tested with PG versions from 7.4 to 8.3b2, with any server
'standard_conforming_strings' setting and with 'PSYCOPG_OWN_QUOTING' too.