DERBY-6626: Check type of user-supplied modules before creating instances

Make SequenceUpdater verify that the class specified by the
derby.language.sequence.preallocator property is a
SequencePreallocator before attempting to create an instance of it.

Make dblook and ij verify that user-specified JDBC driver class names
and DataSource class names implement the correct interfaces before
attempting to create and use them.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1607795 13f79535-47bb-0310-9956-ffa450edef68