private void openWithToolStripMenuItem_Click(object sender, EventArgs e)
{
var item = GitTree.SelectedNode.Tag;
var gitItem = item as GitItem;
if (gitItem == null || !(gitItem).IsBlob)
return;
var fileName = Path.Combine(Module.WorkingDir, (gitItem).FileName);
OsShellUtil.OpenAs(fileName.ToNativePath());
}