Function git_features::threading::upgrade_ref_to_mut

pub fn upgrade_ref_to_mut<'a, T>(
    v: RwLockUpgradableReadGuard<'a, T>, 
    _orig: &'a MutableOnDemand<T>
) -> RwLockWriteGuard<'a, T>

Upgrade a handle previously obtained with get_ref_upgradeable() to support mutation.