[Ada] Fix error detection for anonymous access types

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on HEAD

In case of anonymous access types the null-exclusion and access-to
constant attributes must match. For example:
--
package Test is
   procedure F11 (Ref : not null access Integer);
   procedure F15 (Ref : access constant Integer);
end Test;
package body Test is
   procedure F11 (Ref : access Integer) is     -- Error
   begin
      null;
   end F11;
   procedure F15 (Ref : access Integer) is     -- Error
   begin
      null;
   end;
end Test;
--
The correct output of this test are the following error messages:
  test.adb:3:14: not fully conformant with declaration at test.ads:2
  test.adb:3:14: type of "Ref" does not match
  test.adb:8:14: not fully conformant with declaration at test.ads:3
  test.adb:8:14: type of "Ref" does not match

2005-09-01  Javier Miranda  <miranda@adacore.com>
	    Gary Dismukes  <dismukes@adacore.com>

	* sem_ch6.ads, sem_ch6.adb (Check_Conformance): In case of anonymous
	access types the null-exclusion and access-to-constant attributes must
	also match.
	(Analyze_Return_Statement): When the result type is an anonymous access
	type, apply a conversion of the return expression to the access type
	to ensure that appropriate accessibility checks are performed.
	(Analyze_Return_Type): For the case of an anonymous access result type,
	generate the Itype and set Is_Local_Anonymous_Access on the type.
	Add ??? placeholder for check to disallow returning a limited object
	in Ada 2005 unless it's an aggregate or a result of a function call.
	Change calls from Subtype_Mark to Result_Definition.
	(Analyze_Subprogram_Body): Change formal Subtype_Mark to
	Result_Definition in call to Make_Function_Specification.
	(Build_Body_To_Inline): Change Set_Subtype_Mark to
	Set_Result_Definition.
	(Make_Inequality_Operator): Change formal Subtype_Mark to
	Result_Definition in call to Make_Function_Specification.
	(Process_Formals): Create the new null-excluding itype if required.
	(New_Overloaded_Entity): For an entity overriding an interface primitive
	check if the entity also covers other abstract subprograms in the same
	scope. This is required to handle the general case, that is, overriding
	other interface primitives and overriding abstract subprograms inherited
	from some abstract ancestor type.
	(New_Overloaded_Entity): For an overriding entity that comes from
	source, note the operation that it overrides.
	(Check_Conformance, Type_Conformant): Addition of one new formal
	to skip controlling formals in the analysis. This is used to
	handle overloading of abstract interfaces.
	(Base_Types_Match): Add missing case for types imported from
	limited-with clauses
	(New_Overloaded_Entity): Add barrier to protect the use of
	the "alias" attribute.

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