The error message when a web service can't be found totally unhelpful

Currently, if the class cannot be found, the entire text of the message is:

Cannot find external class

This is ... not very helpful. I propose to change it to

'Cannot find external class ' . $function->classname

and I am wording this as a bug, because I think it is worth doing on stables too.

I was struggling to diagnose a bug we were seeing, so first I just hacked this change into our code. Then I decided to do the socially responsible thing and submit it upstream.