Setters on JaxenXPathExpression have no effect on the underlying DOMXPath object

The setter methods of JaxenXPathExpression (for fields other than the xpathObject)
only set the private field of the JaxenXPathExpression. The new values are not
propagated to the xpathObject and therefore have no effect.

The method "afterPropertiesSet()" probably was initially designed for this purpose,
but it is only called in the constructor. Besides that, this method would have no
effect if called in the setter methods, because it does nothing if the xpathObject
is not null (i.e. after the first call).

The bug was found in the following use case:

Namespace prefixes in an XPath expression within a <jbi:condition> element in
a drools rule are not recognized when the expression is evaluated.

This should work, since the JaxenConditionFactory correctly sets the namespace
context in the JaxenXPathExpression object. But because of the bug, the
namespace context in the DOMXPath object is not set.