Clone - Poor diagnostics on missing tool registration

This is a port from a patch made against SAK-7004. We've been running it for around a year at Michigan. Helps catch some errors when running in production (NPE check). Should have been merged in a long time ago. Please merge.

The diagnostics from Sakai on attempting to dispatch to a missing or improperly registered tool context have always been extremely poor.

WARN: Bug Report user: admin usage-session: 11ea2976-60bc-4e82-807b-d507d5b9000e time: 2006/10/26 18:52:48 user comment: null stack trace
java.lang.NullPointerException
at org.sakaiproject.tool.impl.ActiveToolComponent$MyActiveTool.forward(ActiveToolComponent.java:339)
at org.sakaiproject.portal.charon.CharonPortal.forwardTool(CharonPortal.java:1632)

etc. etc.

The lines in question are

getDispatcher().forward(wreq, wres);

at ActiveToolComponent.java (around line 339) making a call to:

protected RequestDispatcher getDispatcher()
{
return m_servletContext.getNamedDispatcher(getId());
}