Modified DBField.setValue() to avoid minor information leakage.

Previously, I was reporting that setValue() was being called on a
Vector field before checking the permissions to call setValue().

Now, the caller will get the same error when calling setValue() on a
Vector or non-Vector field that the caller lacks permission to change.
Tweaked adminSession, GanymedeAdmin javadocs
Tried to fix logout logging for admin console disconnect.
Let's log admin console disconnects to stderr/admin consoles.

This makes for symmetry with the admin console connects.
And make the admin disconnect message symemtric with admin connect.