Introducing TrackingCursor which knows it's current position

src/PostgresDriver/Cursor.php

src/PostgresDriver/CursorException.php

src/PostgresDriver/ICursor.php

src/PostgresDriver/TrackedCursor.php

tests/Store/PostgresDriver/CursorInterfaceTest.php

tests/Store/PostgresDriver/CursorTest.phpt

tests/Store/PostgresDriver/FastCursorTest.phpt

tests/Store/PostgresDriver/TrackedCursorTest.phpt