--------------------------
	Add a rule-check pass
	(special request by Manuel)
	--------------------------

	DO NOT merge with stable

The flag

	-frule-check foo

will report all sites at which RULES whose name starts with "foo.."
might apply, but in fact the arguments don't match so the rule
doesn't apply.

The pass is run right after all the core-to-core passes.  (Next thing
to do: make the core-to-core script external, so you can fiddle with
it.  Meanwhile, the core-to-core script is in
	DriverState.builCoreToDo
so you can move the CoreDoRuleCheck line around if you want.

The format of the report is experimental: Manuel, feel free to fiddle
with it.

Most of the code is in specialise/Rules.lhs


Incidental changes
~~~~~~~~~~~~~~~~~~
Change BuiltinRule so that the rule name is accessible
without actually successfully applying the rule.  This
change affects quite a few files in a trivial way.