sem_attr.adb (Analyze_Attribute, [...]): Add restrictions to the prefix of 'Old.

sem_attr.adb (Analyze_Attribute, [...]): Add restrictions to the prefix of 'Old.

    gcc/ada/
	* sem_attr.adb (Analyze_Attribute, Attribute_Old case): Add
	restrictions to the prefix of 'Old.
	* sem_util.ads, sem_util.adb (In_Parameter_Specification): New.
	* gnat_rm.texi ('Old): Note that 'Old cannot be applied to local
	variables.

    gcc/testsuite/
	* gnat.dg/old_errors.ads, gnat.dg/old_errors.adb: New.

Co-Authored-By: Robert Dewar <dewar@adacore.com>
From-SVN: r135282