Fix handling of JDBC types NCHAR, NVARCHAR and LONGNVARCHAR

The JDBC types NCHAR, NVARCHAR and LONGNVARCHAR have been introduced
with JDBC 4 (i.e. Java SE 6 ). Regarding programming logic, they should
be treated as their non-unicode counterparts CHAR, VARCHAR and
LONGVARCHAR. I added the new datatypes to the programming logic where
needed.

See bug 402516.

Signed-off-by: Sabine Heider <sabine.heider@sap.com>