Explicitly make name column use type text for mdb2

oracle uses MDB2 for all db queries. The problem is MDB2 tries to guess the type of query variables is the type is not specified explicitly. That causes folders like `2013-04-24` to break the filecache because the name is inserted into the filecache as `2013-04-24 00:00:00`.

well ... only OC5 on oracle is affected. OC6 on oracle is working fine.

@DeepDiver1975 @karlitschek @craigpg @icewind1991 @bartv2  I created the PR here because it makes folders unusable. With this PR rescanning will repair the broken filecache.