[Ada] xref improvements

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

Minor code clean ups.
Add cross xref support for interfaces, for e.g. source nagivation in IDEs.

2007-04-06  Ed Schonberg  <schonberg@adacore.com>
	    Javier Miranda  <miranda@adacore.com>

	* lib-xref.ads, lib-xref.adb: 
	Modify the loop that collects type references, to include interface
	types that the type implements. List each of these interfaces when
	building the entry for the type.
	(Generate_Definition): Initialize component Def and Typ of new entry
	in table Xrefs, to avoid to have these components unitialized.
	(Output_References): Split Is_Abstract flag into
	Is_Abstract_Subprogram and Is_Abstract_Type.
	(Generate_Reference): Add barrier to do not generate the warning
	associated with Ada 2005 entities with entities generated by the
	expander.

Attachment: difs
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