(not only) LDAP Oracle compatiblity

Might be not perfect, yet. Please take a good look at lib/db.php  in peculiar. The additions are required for a save transition from  non-nullable-clob of configvalue to a nullable one in Oracle. Requires testing with other DBs yet. The part could be in Updater as well, but updateDbFromStructure feels more appropriate to me.

There is also a version bump in lib/util.php to trigger the DB change for now. @karlitschek for next release you can go with 5.00.16 as usual.

@butonic @bartv2 

@MTRichards you could try this already with your setup.