request to add missing jdbc jars, at least postgres.jar

[Harmeet Bedi]

/framework/entity/lib contains only derby jdbc library. Wondering if it 
makes sense to enhance it to include other popular jar files.
We run ofbiz against postgres and have to copy the jar file.
It should be easy to add popular jdbc jar files at least when requested 
by someone who needs it. Won't cause conflicts and make life easier for 
people working on ofbiz.

If this seems ok.. and if you want i can file an issue and attach the 
most appropriate current postgres jar to issue.

Harmeet