Add support for retrieving foreign keys with the MySQL client
Add support for retrieving foreign keys with the SQLite client

As noted here: http://www.sqlite.org/foreignkeys.html#fk_enable, not all
databases support foreign keys. However unless SQLITE_OMIT_FOREIGN_KEY
was included during compilation of sqlite, the foreign_key_list pragma
will still list the foreign keys even if they are not enforced.
Add support for retrieving foreign keys with the Oracle client
Add support for specifying the non-default schema in the Oracle client

This will query the `ALL_*` tables when fetching the tables or views
Remove trailing whitespace