Added support to directly connect also to Microsoft SQL Server database.

Fixed direct connection to always use the same query as of UNION query SQL injection (= one query with multiple columns/entries output).
Minor fixes to Firebird/Access/SQLite connectors to use connector's execute()/fetchall() as wrapper for third-party libraries' methods.
Forced conf.timeout to 10 seconds when directly connecting to database.
Slightly improved regular expression to parse -d parameter.
Added import check for all connectors' third-party libraries.
Code refactoring:
* Moved conf.direct request to direct() function in lib/request/direct.py (code reused where needed).
* Back-delegated to generic connector close() and other methods.