Generified BeanComparator.

Note that not all type-safety warnings can be fixed because the actual type
of the properties to be compared is only known at runtime.
The test class was also reworked; unneccessary try-catch-blocks were removed.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/beanutils/branches/java5@1538224 13f79535-47bb-0310-9956-ffa450edef68