sem_ch5.adb: Improve warnings on redundant assignments

sem_ch5.adb: Improve warnings on redundant assignments

2007-08-14  Robert Dewar  <dewar@adacore.com>
	    Ed Schonberg  <schonberg@adacore.com>

	* sem_ch5.adb: Improve warnings on redundant assignments

	* sem_util.ads, sem_util.adb: (Is_Variable): Add defense against junk
	parameter
	(Is_Synchronized_Tagged_Type): New subprogram that returns true
	in case of synchronized tagged types (AARM 3.9.4 (6/2)).
	(Safe_To_Capture_Value): Can now return True for constants, even if Cond
	is set to False. Improves handling of Known_[Not_]Null.
	(Wrong_Type): Special case address arithmetic attempt
	(Collect_Abstract_Interfaces): Add new formal to allow collecting
	abstract interfaces just using the partial view of private types.
	(Has_Abstract_Interfaces): Add new formal to allow checking types
	covering interfaces using the partial view of private types.
	(Is_Fully_Initialized_Type): Special VM case for uTag component. This
	component still needs to be defined in this case, but is never
	initialized as VMs are using other dispatching mechanisms.
	(Abstract_Interface_List): For a protected type, use base type to get
	proper declaration.
	Improve warnings on redundant assignments
	(Is_Variable): Handle properly an implicit dereference of a prefixed
	function call.
	(Build_Actual_Subtype): If this is an actual subtype for an
	unconstrained formal parameter, use the sloc of the body for the new
	declaration, to prevent anomalises in the debugger.

From-SVN: r127427