Add support for Java 8 Date and Time API AKA JSR-310. On the face of it
the existing JDBC types java.sql.Date, java.sql.Time and
java.sql.Timestamp offer conversion methods to and from JSR-310 data
types. Unfortunately java.sql.Timestamp does silent data truncation
when the timestamp falls into a DST transition on the JVM time zone.
Worse still for java.time.OffsetDateTime there is no corresponding JDBC
type. Therefore these conversions have to be implemented. All of this
has to be programmed using reflection so the code compiles and can be
executed on Java 7.

Fix bug in picking the right index for INSERT..ON DUPLICATE KEY UPDATE when there are both UNIQUE and PRIMARY KEY constraints.

It's already implemented and working:
https://github.com/h2database/h2database/pull/150

Since we now require at least Java 6 we can remove the Java 6 backwards
compatibility layer.

The current implementation of getObject does not support byte[]. This
is an issue for some people [1].

 [1] https://groups.google.com/forum/#!topic/h2-database/InWprFw2B0o

Some of the existing JDBC code is missing guards around debug
statements that allocate strings.

Implemented unit test.

I found the comments in TimestampWithTimeZone not helpful in
understanding the semantics of the public methods.

This commit includes the following changes

 - add comments to previously not commented public methods in
   TimestampWithTimeZone that describe the semantics
 - add more verifications to TestTimeStampWithTimeZone to make sure the
   actual behavior matches the documented behavior

The convenience accessors getYear getMonth and getDay in
TimestampWithTimeZone return long even though their values fall within
the range of int. This makes them a bit inconvenient to work with as
most APIs (Calendar, LocalDateTime) take int for such values.

This commit contains the following changes

 - change TimestampWithTimeZone#getYear() to return an int instead of
   a long
 - change TimestampWithTimeZone#getMonth() to return an int instead of
   a long
 - change TimestampWithTimeZone#getDay() to return an int instead of
   a long

Both JdbcResultSet and JdbcCallableStatement currently do not support
getObject(int, Class) and getObject(String, Class) but support is easy
to add.

This commits contains the following changes:

 - add support for getObject(int, Class) and getObject(String, Class)
    with the following types: BigDecimal, String, Boolean, Byte, Short,
   Integer, Long, Float, Double, Date, Time, Timestamp, UUID,
   TimestampWithTimeZone and Geometry subclasses
 - extend the existing getObject tests to cover these new methods

Most notably missing is support for LOBs and arrays including primitive
arrays but this can always be added later.