* 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.
return value for partially parsed time values.
* psycopg/typecast_mxdatetime.c (typecast_MXDATE_cast): return
NULL after setting DataError. Also, don't treat it as an error if
typecast_parse_time() returns 0 (as might happen if the remainder
of the string is " BC").
* psycopg/typecast_datetime.c (typecast_PYDATE_cast): return NULL
after setting DataError.
(typecast_PYDATETIME_cast): same here.
(typecast_PYTIME_cast): same here.
* tests/test_dates.py
(CommonDatetimeTestsMixin.test_parse_incomplete_date): test that
parsing incomplete date values results in DataError.
(CommonDatetimeTestsMixin.test_parse_incomplete_time): same for
times.
(CommonDatetimeTestsMixin.test_parse_incomplete_time): same for
datetimes.
* tests/test_dates.py: add tests for date/time typecasting and
adaption.
* psycopg/adapter_mxdatetime.c (mxdatetime_str): add support for
outputting BC dates (which involves switching them to one-based
dates). Also remove broken handling of microseconds.
* psycopg/typecast.c (typecast_parse_date): if the string ends
with "BC" adjust the year value to be a zero-based BC value as
used by mx.DateTime (datetime doesn't support BC dates).
(typecast_parse_time): ignore ' ', 'B' and 'C' in time strings
rather than treating them as part of the seconds part of the time.
