patchDon't allow others to instantiate NullProgressMonitor

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/NullProgressMonitor.java b/org.spearce.jgit/src/org/spearce/jgit/lib/NullProgressMonitor.java
index 191dc00..1c30e6b 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/NullProgressMonitor.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/NullProgressMonitor.java
@@ -45,6 +45,10 @@
 	/** Immutable instance of a null progress monitor. */
 	public static final NullProgressMonitor INSTANCE = new NullProgressMonitor();
 
+	private NullProgressMonitor() {
+		// Do not let others instantiate
+	}
+	
 	public void start(int totalTasks) {
 		// Do not report.
 	}