disallow other package's names in struct field dot.

R=ken
OCL=22996
CL=22996

src/cmd/gc/dcl.c

@@ -512,6 +512,8 @@ loop:
 		f->nname = n->left;
 		f->embedded = n->embedded;
 		f->sym = f->nname->sym;
+		if(pkgimportname != S && !exportname(f->sym->name))
+			f->sym = pkglookup(f->sym->name, pkgimportname->name);
 	}
 
 	*t = f;

src/cmd/gc/go.h

@@ -741,6 +741,7 @@ void	constiter(Node*, Type*, Node*);
  */
 void	renamepkg(Node*);
 void	autoexport(Sym*);
+int	exportname(char*);
 void	exportsym(Sym*);
 void	packagesym(Sym*);
 void	dumpe(Sym*);

src/cmd/gc/go.y

@@ -160,6 +160,7 @@ import_there:
 	{
 		checkimports();
 		unimportfile();
+		pkgimportname = S;
 	}
 |	LIMPORT '$' '$' hidden_import_list '$' '$'
 	{