Exposing names in extensions to make the datetime tests run
Added test to verify infinity parsing in dates

Test currently failing. Added by @intgr as psycopg-ctypes issue #30. To be
added to upstream test suite.
Fixed parsing of infinity date/timestamp
Raise DataError upon bad date values
Raise ValueError on BC dates
Fixed typo in tests names
Fixed parsing of negative tz offset

Also make sure to handle sub-minute offset the same way psycopg2 does for the
sake of test passing.
Added microseconds adaptation of timedelta objects
C-style interval parsing algorithm replaced by regexp
Dropped math.pow use in time parsing
Oops... fixed year length