prj-attr.adb (Package_Node_Id_Of): Returns Unknown_Package when package is not known

prj-attr.adb (Package_Node_Id_Of): Returns Unknown_Package when package is not known

2007-12-19  Vincent Celier  <celier@adacore.com>

	* prj-attr.adb (Package_Node_Id_Of): Returns Unknown_Package when
	package is not known

	* prj-attr.ads (Unknown_Package): New constant
	Do not crash when an unknown package is in several projects

	* prj-dect.adb (Parse_Package_Declaration): Mark an unknown package as
	ignored

	* prj-nmsc.adb (Check): Remove obsolete code related to no longer
	existing package Language_Processing.

From-SVN: r131078