By Jonathan Landay FRONTLINE WEST OF KHERSON, Ukraine (Reuters) – Oleh, the commander of a Ukrainian mechanized infantry unit dug into trenches west of Kherson, is confident his Russian foes will be forced to abandon the strategic port by winter weather, logistical logjams and the threat of encirclement. But neither he nor his men think the Russians will go quickly or quietly and nor do they intend to let them. His comments raise the spectre of a bloody slog in the coming weeks for control of a key city on the west bank of the Dnipro River which acts as a gateway to the peninsula of Crimea ann…