Major code refactoring and commenting to detection engine.
Ask user whether or not to proceed to test remaining parameters after an injection point has been identified.
Restore beep at SQL injection find.
Avoid reuse of same variable in DBMS handler code.
Minor adjustment of payloads XML file.
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.
