lib-xref-alfa.adb (Generate_Dereference): Use Get_Code_Unit instead of Get_Source_Uni...

lib-xref-alfa.adb (Generate_Dereference): Use Get_Code_Unit instead of Get_Source_Unit to get file for reference.

2012-03-30  Yannick Moy  <moy@adacore.com>

	* lib-xref-alfa.adb (Generate_Dereference): Use Get_Code_Unit
	instead of Get_Source_Unit to get file for reference.
	(Traverse_Compilation_Unit): Do not add scopes for generic units.
	* lib-xref.adb (Generate_Reference): Use Get_Code_Unit instead
	of Get_Source_Unit to get file for reference.
	* sem_ch12.adb (Analyze_Package_Instantiation): Enable
	instantiation in Alfa mode.

From-SVN: r186002