Fix alignment of GIN in-line posting lists stored in entry tuples.

The Sparc machines in the buildfarm are crashing because of misaligned
access to posting lists stored in entry tuples.

I accidentally removed a critical SHORTALIGN() from ginFormTuple, as part
of the packed posting lists patch. Perhaps I thought it was unnecessary,
because the index_form_tuple() call above the SHORTALIGN already aligned
the size, missing the fact that the null-category byte makes it misaligned
again (I think the SHORTALIGN is indeed unnecessary if there's no null-
category byte, but let's just play it safe...)

Author: hlinnaka

src/backend/access/gin/ginentrypage.c

@@ -87,6 +87,8 @@ GinFormTuple(GinState *ginstate,
 		newsize = Max(newsize, minsize);
 	}
 
+	newsize = SHORTALIGN(newsize);
+
 	GinSetPostingOffset(itup, newsize);
 	GinSetNPosting(itup, nipd);