Fixes #49: load lazy attributes used for filtering in declarative queries
update alldatatypes.py test script
Pass provider to converter.__init__()
Now Pony doesn't set a default varchar max length in SQLite and PostgreSQL. Increase default max len from 200 to 1000 for Oracle and to 255 for MySQL
Changelog updated
Change Pony ORM version: 0.5.post1 -> 0.5.1
Pony ORM release 0.5.1

# Changes/features:

Before this release, if a text attribute was defined without the max length specified (e.g. `name = Required(unicode)`), Pony set the maximum length equal to 200 and used SQL type `VARCHAR(200)`. Actually, PostgreSQL and SQLite do not require specifying the maximum length for strings. Starting with this release such text attributes are declared as `TEXT` in SQLite and PostgreSQL. In these DBMSes, the `TEXT` datatype has the same performance as `VARCHAR(N)` and doesn't have arbitrary length restrictions.

For other DBMSes default varchar limit was increased up to 255 in MySQL and to 1000 in Oracle.

# Bugfixes:

* Correct parsing of datetime values with T separator between date and time
* Entity.delete() bug fixed
* Lazy attribute loading bug fixed