preface only relative names (such as "#foo") with "./".
without this fix, tar was unable to create archives
using absolute path names.

Notes:
Mon Dec 20 12:51:59 EST 2004 rsc
    don't think this is right -- makes it too hard
    to untar tars with absolute names into .
    
    the unix tar agrees with the old behavior.


Reference: /n/sources/patch/applied/tar-abs-names
Date: Tue Dec 21 06:31:59 CET 2004
Reviewed-by: rsc

--- /sys/src/cmd/tar.c	Tue Dec 21 06:32:00 2004
+++ /sys/src/cmd/tar.c	Tue Dec 21 06:31:59 2004
@@ -455,8 +455,10 @@
 		fprint(2, "tar: %s: name too long (max %d)\n", sname, sizeof shortname - 3);
 		return;
 	}
-	
-	snprint(shortname, sizeof shortname, "./%s", sname);
+	if (sname[0] != '/')		/* protect relative names like #foo */
+		snprint(shortname, sizeof shortname, "./%s", sname);
+	else
+		strcpy(shortname, sname);
 	infile = open(shortname, OREAD);
 	if (infile < 0) {
 		fprint(2, "tar: %s: cannot open file - %r\n", longname);