Make - read compressed data from stdin (thanks to Marius Groeger).
diff --git a/archival/gunzip.c b/archival/gunzip.c
index 6f5e63d..c39814d 100644
--- a/archival/gunzip.c
+++ b/archival/gunzip.c
@@ -110,7 +110,7 @@
 	}
 
 	/* Set input filename and number */
-	if (argv[optind] == NULL) {
+	if (argv[optind] == NULL || strcmp(argv[optind], "-") == 0) {
 		flags |= gunzip_to_stdout;
 		in_file = stdin;
 	} else {