exp_ch4.adb (Expand_N_Indexed_Component): For an indexed component with an implicit dereference as its prefix...

	* exp_ch4.adb (Expand_N_Indexed_Component): For an indexed component
	with an implicit dereference as its prefix, use
	Insert_Explicit_Dereference instead of merely rewriting the prefix into
	an explicit dereference. This ensures that a reference to the original
	prefix is generated, if appropriate.

	* sem_util.adb (Insert_Explicit_Dereference): When an implicit
	dereference is rewritten to an explicit one, generate a reference to
	the entity denoted by its prefix using the original prefix node, so
	the dereference can be properly recorded as a read of the denoted
	access value, if appropriate.

	* sem_warn.adb (Output_Unreferenced_Messages): Do not abstain from
	emitting 'assigned but never read' warning on a variable on the basis
	that it has an access type.
	(Check_References): Emit unreferenced warning when the scope is a
	subprogram body.

From-SVN: r91881