CleanCommand: don't fire WorkingTreeModifiedEvent on dry run

Since no files are actually deleted it makes no sense to fire such an
event.

Change-Id: I66e87afc1791f27fddaa873bafe8bb8b61662535
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit/src/org/eclipse/jgit/api/CleanCommand.java

@@ -136,7 +136,7 @@ public class CleanCommand extends GitCommand<Set<String>> {
 		} catch (IOException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		} finally {
-			if (!files.isEmpty()) {
+			if (!dryRun && !files.isEmpty()) {
 				repo.fireEvent(new WorkingTreeModifiedEvent(null, files));
 			}
 		}