[BEANUTILS-456] Provide another method for querying a write method.

PropertyUtilsBean.getWriteMethod(PropertyDescriptor) may fail for properties
obtained via custom bean introspection. Added a warning to the Javadocs. The
method PropertyUtilsBean.getWriteMethod(Class, PropertyDescriptor) was made
public because it works correctly in this case.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/beanutils/trunk@1555231 13f79535-47bb-0310-9956-ffa450edef68
[BEANUTILS-456] Updated changes.xml.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/beanutils/trunk@1555232 13f79535-47bb-0310-9956-ffa450edef68