namet.ads, namet.adb (wn): Improve this debugging routine.

namet.ads, namet.adb (wn): Improve this debugging routine.

2007-04-06  Robert Dewar  <dewar@adacore.com>

	* namet.ads, namet.adb (wn): Improve this debugging routine. Calling
	it no longer destroys the contents of Name_Buffer or Name_Len and
	non-standard and invalid names are handled better.
	(Get_Decoded_Name_String): Improve performance by using
	Name_Has_No_Encodings flag in the name table.
	(Is_Valid_Name): New function to determine whether a Name_Id is valid.
	Used for debugging printouts.

From-SVN: r123586