s3: update docs to discourage use of v2 auth - fixes #2120

From testing it appears that CEPH no longer works properly with v2
auth and neither does Dreamhost, so update the docs anc configuration
to recommend v4 auth.

backend/s3/s3.go

@@ -74,7 +74,7 @@ func init() {
 			Help: "AWS Secret Access Key (password) - leave blank for anonymous access or runtime credentials.",
 		}, {
 			Name: "region",
-			Help: "Region to connect to.",
+			Help: "Region to connect to.  Leave blank if you are using an S3 clone and you don't have a region.",
 			Examples: []fs.OptionExample{{
 				Value: "us-east-1",
 				Help:  "The default endpoint - a good choice if you are unsure.\nUS Region, Northern Virginia or Pacific Northwest.\nLeave location constraint empty.",
@@ -119,10 +119,7 @@ func init() {
 				Help:  "South America (Sao Paulo) Region\nNeeds location constraint sa-east-1.",
 			}, {
 				Value: "other-v2-signature",
-				Help:  "If using an S3 clone that only understands v2 signatures\neg Ceph/Dreamhost\nset this and make sure you set the endpoint.",
-			}, {
-				Value: "other-v4-signature",
-				Help:  "If using an S3 clone that understands v4 signatures set this\nand make sure you set the endpoint.",
+				Help:  "Use this only if v4 signatures don't work, eg pre Jewel/v10 CEPH.\nSet this and make sure you set the endpoint.",
 			}},
 		}, {
 			Name: "endpoint",