Bug 26699 Create Jar fails with no warning if jar read-only
Once *.jardesc has been created, if I invoke "Create JAR" from the context menu and the jar file already exists and is read-only, the progress dialog flashes and nothing more happens. Please add check for this condition and at least an error message should be displayed. Even better, ask something like "Jar file read-only, overwrite?" Y/N and overwrite the file on yes (similar to what the option "warn if jar file exists" does).
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/jarpackager/JarFileExportOperation.java
}
		return (IFile[])unsavedFiles.toArray(new IFile[unsavedFiles.size()]);
	}
	/**
	 * Asks the user to confirm to save the modified resources.
	 * 
	 * @return true if user pressed OK.
	 */
	private boolean confirmSaveModifiedResources(IFile[] dirtyFiles) {
		if (dirtyFiles == null || dirtyFiles.length == 0)
			return true;
		
		Display display= fParentShell.getDisplay();
		if (display == null || display.isDisposed())
			return false;
		
		final ConfirmSaveModifiedResourcesDialog dlg= new ConfirmSaveModifiedResourcesDialog(fParentShell, dirtyFiles);
		final int[] intResult= new int[1];
		Runnable runnable= new Runnable() {
			public void run() {
				intResult[0]= dlg.open();
			}
		};
		display.syncExec(runnable);
		return intResult[0] == IDialogConstants.OK_ID;
	}
	/**
	 * Asks to confirm to save the modified resources
	 * and save them if OK is pressed.
	 *