Cleanups to extr.c and pdfattach

1. In extr.c the error message should use the correct full pathname, not
the base filename.
2. In pdfattach the check for existence of input files should be
replaced with the check for read access to them.

extr.c

@@ -59,7 +59,7 @@ int save_attachments(int pageno, char *targetdir)
 					sprintf(pathname, "%s/%s", targetdir, name);
 					FILE *fout = fopen(pathname, "w");
 					if (!fout) {
-						fprintf(stderr, "extr: cannot write to file %s\n", name);
+						fprintf(stderr, "extr: cannot write to file %s\n", pathname);
 						exit(1);
 					}
 					dump_stream(pdf_to_num(f_obj), fout);

utils/pdfattach

@@ -67,7 +67,7 @@ numargs=$#
 for ((i=1 ; i <= $numargs ; i++))
 do
 	fullname=$(readlink -f "$1")
-	if [ ! -f "$fullname" ] ; then
+	if [ ! -r "$fullname" ] ; then
 		echo "$progname: file \"$fullname\" does not exist" >&2
 		usage
 	fi