Logic for checking character encoding with Oracle DB is wrong in server and frontend.

Oracle has two character set variables that we check: NLS_CHARACTERSET & NLS_NCHAR_CHARACTERSET.

We check that both of these are UTF8, which is wrong.

1. Oracle uses UTF8 name for CESU-8. Proper UTF8 encoding is called AL32UTF8.
2. We assume that both NLS_CHARACTERSET & NLS_NCHAR_CHARACTERSET have the same value. This may not be the case.

Suggest allowing AL32UTF8 & UTF8 (CESU-8). The latter should be supported for backwards compatibility with existing installations.