ug_words, [...]: Added alpha-ivms transitioning section to porting guide chapter...

ug_words, [...]: Added alpha-ivms transitioning section to porting guide chapter (vms version).

	* ug_words, gnat_ugn.texi: Added alpha-ivms transitioning section to
	porting guide chapter (vms version).
	Revised doc title (removed "for native platforms") and subtitle.
	Add discussion on warning flag for obsolescent features. First we
	note that it applies to obsolete GNAT features, which was previously
	omitted. Second we contrast the behavior with that of the new
	Ada 2005 AI-368 restriction No_Obsolescent_Features.
	Preliminary rewriting of GNAT & libraries chapter in order to take
	into account default project locations & new project manager
	capabilities.

	* cstand.adb (Create_Operators): Clean up format and documentation of
	unary and binary operator result tables. No change in code, just
	reformatting and addition of comments.

	* errout.ads, gnatfind.adb, s-maccod.ads, sem.adb,
	sem_ch2.adb: Minor reformatting

	* atree.ads, elists.ads, lib.ads, namet.ads, nlists.ads, repinfo.ads,
	sinput.ads, stringt.ads, uintp.ads, urealp.ads: Minor clarification to
	comments for Tree_Read and Tree_Write.

	* exp_attr.ads: Minor reformatting.

	* comperr.adb (Compiler_Abort): Add specialized message for GAP
	versions.

	* exp_pakd.adb (Create_Packed_Array_Type): Add a guard to check
	whether the ancestor type is private, as may be the case with nested
	instantiations.

From-SVN: r92852