Fixed #23108 -- Dropped support for PostgreSQL 8.4 & PostGIS 1.3, 1.4.

In fact, a more important requirement of OSMGeoAdmin is to have GDAL installed. Then, the 900913 projection only needs to be manually installed if GDAL is lower than 1.7 (1.6 being the only still-supported version in this case, and I doubt many people are still using it).