func (file *GridFile) SetName(name string) {
	file.assertMode(gfsWriting)
	file.m.Lock()
	file.doc.Filename = name
	file.m.Unlock()
}
func (file *GridFile) SetName(name string) {
	file.assertMode(gfsWriting)
	file.m.Lock()
	file.doc.Filename = name
	file.m.Unlock()
}
// SetName changes the optional file name.  An empty string may be used to
// unset it.
//
// It is a runtime error to call this function when the file is not open
// for writing.