func (file *GridFile) SetUploadDate(t time.Time) {
	file.assertMode(gfsWriting)
	file.m.Lock()
	file.doc.UploadDate = t
	file.m.Unlock()
}
func (file *GridFile) SetUploadDate(t time.Time) {
	file.assertMode(gfsWriting)
	file.m.Lock()
	file.doc.UploadDate = t
	file.m.Unlock()
}
// SetUploadDate changes the file upload time.
//
// It is a runtime error to call this function when the file is not open
// for writing.