s3: Storj provider: fix server-side copy of files bigger than 5GB

Like some other S3-compatible providers, Storj does not currently
implements UploadPartCopy and returns NotImplemented errors for
multi-part server side copies.

This patch works around the problem by raising --s3-copy-cutoff for
Storj to the maximum. This means that rclone will never use
multi-part copies for files in Storj. This includes files larger than
5GB which (according to AWS documentation) must be copied with
multi-part copy. This works fine for Storj.

See https://github.com/storj/roadmap/issues/40

backend/s3/s3.go

@@ -3470,6 +3470,10 @@ func setQuirks(opt *Options) {
 			opt.ChunkSize = 64 * fs.Mebi
 		}
 		useAlreadyExists = false // returns BucketAlreadyExists
+		// Storj doesn't support multi-part server side copy:
+		// https://github.com/storj/roadmap/issues/40
+		// So make cutoff very large which it does support
+		opt.CopyCutoff = math.MaxInt64
 	case "Synology":
 		useMultipartEtag = false
 		useAlreadyExists = false // untested