log4j detection broken in OSGi

This was introduced by a change in JBLOGGING-94

The test for log4j was changed from:

Class.forName("org.apache.log4j.Hierarchy", true, cl);

to:

Class.forName("org.apache.log4j.config.PropertySetter", true, cl);

However the OSGi package imports where not updated to also include "org.apache.log4j.config". And this the latter test for "PropertySetter" will always fail in OSGi.

The fix should be pretty simple. Simply import "org.apache.log4j.config" as optional in addition.