printenv: exit status is 2 on failure

This provides a reliable and portable way to
test whether an environment variable is defined.

(Of course, if you are using glibc you may get
false positives if you include a = in the query.)

Signed-off-by: Mattias Andrée <maandree@kth.se>

printenv.c

@@ -26,5 +26,5 @@ main(int argc, char *argv[])
 		}
 	}
 
-	return fshut(stdout, "<stdout>") || ret;
+	return fshut(stdout, "<stdout>") ? 2 : ret;
 }