The "callable name" may be the same for multiple distinct callables.
The code already worked around this for the case of instance methods,
but there are other cases in which callable names clash, such as
the use of self:: reported in the referenced bug.
Rather than trying to generate a unique name for callables, compare
the content of the alfi structures. This is less efficient if there
are many autoload functions, but autoload *registration* does not
need to be particularly efficient.
As a side-effect, this no longer permits unregistering non-callables.
94df2f697f