Add a new debug procedure psloc, to display a source location.

Tested on x86_64-pc-linux-gnu, committed on trunk

2012-07-17  Tristan Gingold  <gingold@adacore.com>

	* treepr.ads (psloc): Declare.
	* treepr.adb (psloc): New debug procedure to print a sloc.
	(Print_Sloc): New procedure, from ...
	(Print_Node_Subtree): ... this.  Call Print_Sloc.