Export layer data to SQLite becomes too slow

[wyylling]

1. Take the standard WW dump (TB_WW.dump also attached) and import it with TB2011
2. Generate graphic with the standard display model (also attached)
3. In Display manager select WW_Line with the right mouse taste and choose "Export Layer Data to SQLite..."
4. After 2 seconds, the sqlite file is created.
5. Take the same dump and import it with Map 2012 (inclusive structure updates)
6. Generate graphic with the standard display model (also attached)
7. In Display manager select WW_Line with the right mouse taste and choose "Export Layer Data to SQLite..."

Result: After 20 seconds the sqlite file is created. This is 10 times the time that was used with TB 2011

Expected result: The SQLite file should be created after 2 seconds.

[stevenxu]

The fix (r6471) is reverted in r6485 for it is by design and we should reuse all of FDO objects in caller side to gain the performance while inserting many features.