Add injection point information to exception message when injection into observer fails

Injections that fail when an observer method is invoked are massively hard to track down. Here's the information you get:

org.jboss.weld.exceptions.IllegalArgumentException: WELD-001324 Argument bean must not be null
at org.jboss.weld.manager.BeanManagerImpl.getReference(BeanManagerImpl.java:714)
at org.jboss.seam.exception.control.HandlerMethodImpl.notify(HandlerMethodImpl.java:187)
at org.jboss.seam.exception.control.ExceptionHandlerDispatch.executeHandlers(ExceptionHandlerDispatch.java:128)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.jboss.weld.util.reflection.SecureReflections$13.work(SecureReflections.java:305)
at org.jboss.weld.util.reflection.SecureReflectionAccess.run(SecureReflectionAccess.java:54)
at org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInvocation(SecureReflectionAccess.java:163)
at org.jboss.weld.util.reflection.SecureReflections.invoke(SecureReflections.java:299)
at org.jboss.weld.introspector.jlr.WeldMethodImpl.invokeOnInstance(WeldMethodImpl.java:188)
at org.jboss.weld.introspector.ForwardingWeldMethod.invokeOnInstance(ForwardingWeldMethod.java:59)
at org.jboss.weld.injection.MethodInjectionPoint.invokeOnInstanceWithSpecialValue(MethodInjectionPoint.java:198)
at org.jboss.weld.event.ObserverMethodImpl.sendEvent(ObserverMethodImpl.java:270)
at org.jboss.weld.event.ObserverMethodImpl.sendEvent(ObserverMethodImpl.java:253)
at org.jboss.weld.event.ObserverMethodImpl.notify(ObserverMethodImpl.java:222)
at org.jboss.weld.manager.BeanManagerImpl.notifyObservers(BeanManagerImpl.java:632)
at org.jboss.weld.manager.BeanManagerImpl.fireEvent(BeanManagerImpl.java:619)
at org.jboss.weld.manager.BeanManagerImpl.fireEvent(BeanManagerImpl.java:613)

I expect to see the type and qualifiers at the failing injection point.