Generified BeanMap.

Without breaking backwards compatibility, it is only possible to use the
parameters <Object, Object>, rather than the logically correct
<String, Object>. I did not touch the deprecated defaultTransformers field;
so there are still warnings present.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/beanutils/branches/java5@1538223 13f79535-47bb-0310-9956-ffa450edef68