Add missing methods to SQL database and driver classes

This resolves Bug 2121

sip/qtsql/qsqldatabase.sip

@@ -80,6 +80,7 @@ public:
 	bool open() /ReleaseGIL/;
 	bool open(const TQString &,const TQString &) /ReleaseGIL/;
 	void close();
+	bool ping();
 	bool isOpen() const;
 	bool isOpenError() const;
 	TQStringList tables() const;

sip/qtsql/qsqldriver.sip

@@ -74,6 +74,7 @@ public:
 			  const TQString & = TQString::null,
 			  int = -1) = 0 /ReleaseGIL/;
 	virtual void close() = 0;
+	virtual bool ping() = 0;
 	virtual TQSqlQuery createQuery() const = 0;
 
 %If (TQt_3_2_0 -)