Fix: really delete file

src/main/java/com/sheepit/client/Utils.java

@@ -376,4 +376,25 @@ public class Utils {
 		
 		return String.format("%.2f%s", (bytes / divider), suffix);
 	}
+	
+	/**
+	 * Sometimes on Windows, delete of file return false for no obvious reason.
+	 * Wait a bit and try again
+	 */
+	public static boolean deleteFile(File file) {
+		if (file.delete() == false) {
+			// maybe the system was busy
+			try {
+				Thread.sleep(4000);
+			}
+			catch (InterruptedException e) {
+			}
+			System.gc();
+			if (file.delete() == false) {
+				file.deleteOnExit(); // nothing more can be done...
+				return false;
+			}
+		}
+		return true;
+	}
 }