gen_index_id(): New function. Construct an index key such that the sort

gen_index_id():  New function.  Construct an index key such that the sort
	is stable and the form is only defined in one place, since we do
	some fancy footwork with the keys to separate the defining instance
	of a module reference from other references in the HTML index.

make_index_entry():  Override the standard definition to use get_index_id().

make_str_index_entry():  Moved to myformat.perl; only needed there.

index_key_eq():  Override the standard definition.  Add key transforms to
	remove extra junk from the end of the keys; it was only there to
	maintain ordering.

clean_key():  Remove key transform no longer needed at this stage, because
	keeping it makes the sort unstable.

add_idx():  Add key transforms to undo the mess we do to separate a module's
	defining and reference entries.  Don't make the text bold.