Handle namedpipe copy

CopyFile relies on copy.Copy from https://github.com/otiai10/copy which
doesn't handle named pipes copy. Handle it here until
https://github.com/otiai10/copy/issues/47 is fixed.

This causes luet to hang while copying packages that have named pipes in
it.

Also invert compression argument for gzip, it causes slowliness.

pkg/compiler/artifact.go

@@ -373,7 +373,7 @@ func (a *PackageArtifact) Compress(src string, concurrency int) error {
 		}
 		// Create gzip writer.
 		w := gzip.NewWriter(dst)
-		w.SetConcurrency(concurrency, 10)
+		w.SetConcurrency(1<<20, concurrency)
 		defer w.Close()
 		defer dst.Close()
 		_, err = io.Copy(w, bufferedReader)