Patch for saving Table OID and Attribute Number

[calledit]

When columns are renamed in sql queries, tracking the original table and column is not possible in the current implementation.

Example:

SELECT users.user_names AS username, posts.text AS post_text from users
LEFT INNER JOIN posts ON posts.user_id = users.id

In this query the original table will not be accessible, despite postgres acctually returning that information.

This patch adds two propertys to the fieldDesc struct and code to parse those fields from the postgres response.
Originally mentioned in #363

[rafiss]

thanks for the contribution. could you please add a test that confirms it works as expected?