DERBY-5840: Clean up compiler warnings introduced by using Java 5 language features

Refactor ClassSizeCatalog to prevent unchecked conversion warnings when
ClassSize creates an instance via reflection and casts the result to
Hashtable<String, int[]>.

Introduce a new abstract ClassSizeCatalog class and rename the generated
class to ClassSizeCatalogImpl, which extends ClassSizeCatalog. ClassSize
can now access the catalog via the abstract class instead of casting it
unchecked to Hashtable<String, int[]>.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1485322 13f79535-47bb-0310-9956-ffa450edef68