clarified signature;

--- a/src/Pure/System/isabelle_system.scala	Sat May 28 22:33:11 2022 +0200
+++ b/src/Pure/System/isabelle_system.scala	Sun May 29 11:43:13 2022 +0200
@@ -423,19 +423,18 @@
   def rsync(
     cwd: JFile = null,
     progress: Progress = new Progress,
-    echo: Boolean = false,
     verbose: Boolean = false,
     dry_run: Boolean = false,
-    purge: Boolean = false,
+    clean: Boolean = false,
     args: List[String] = Nil
   ): Process_Result = {
     val script =
       "rsync --protect-args --archive" +
         (if (verbose) " --verbose" else "") +
         (if (dry_run) " --dry-run" else "") +
-        (if (purge) " --delete-excluded" else "") +
+        (if (clean) " --delete-excluded" else "") +
         (if (args.nonEmpty) " " + Bash.strings(args) else "")
-    progress.bash(script, cwd = cwd, echo = echo || verbose)
+    progress.bash(script, cwd = cwd, echo = true)
   }
 
   def make_patch(base_dir: Path, src: Path, dst: Path, diff_options: String = ""): String = {