This is necessary because commit 8131a24 (Tue Mar 27 10:08:13 2012) started passing the config section name rather than hardcoding "AssetService"
This meant that the HG external-facing asset service tried to read ConnectionString from [HGAssetService] rather than [AssetService].
On SQLite, not finding this meant that it fell back to [DatabaseService], which is set for OpenSim.db rather than Asset.db.
Therefore, all external asset requests returned null.
Solution taken here is to create an [HGAssetService] section with the same ConnectionString as [AssetService].
This bug does not affect normal MySQL/MSSQL config since they use the [DatabaseService] connection string anyway.
Addresses http://opensimulator.org/mantis/view.php?id=6200, many thanks to DanBanner for identifying the exact problem commit which was very helpful.
This was a regression from OpenSimulator 0.7.3.1 which did not contain this bug.
a533db7e27