TimeDelta support needs improvements

[Gustavo Niemeyer]

TimeDelta support isn't as well tested as the other date/time types, is
broken in SQLite and MySQL, has precision issues in PostgreSQL, and
potentially uses code which conflicts with the license for parsing.

[Gustavo Niemeyer (niemeyer)]

The attached branch fixes all of these issues, and improves the format
accepted by the interval parser.

[Barry Warsaw (barry)]

The branch works great for me. How about committing it? :)

[Jamu Kakar (jkakar)]

Nice branch! +1.

[Christopher Armstrong (radix)]

[1] Is there a reason you don't upcall to Connection.to_database in MySQLConnection.to_database? I guess it would be awkward, since you'd have to iterate the results and re-yield them, but the code duplication is unfortunate.

[2]
Out of curiosity, why did you make these things keyword arguments to _parse_interval? I figured it might've been for testing that function, but it doesn't seem they're used.

+def _parse_interval(interval, _table=_parse_interval_table(),
+ _re=_parse_interval_re):

+1!

[Gustavo Niemeyer (niemeyer)]

[1]

Yes, that's just preventing the creation of the additional generator. I think it's worth it, as it's in
a very internal loop which is used very frequently.

[2]

A silly early optimization. I took it off.

Thanks for these reviews!