By Marc Jones LONDON (Reuters) - The European Central Bank might ease restrictions on how much short-term Greek government debt the country's banks can hold if becomes clear the euro zone will disburse long-awaited aid to Athens, a banking source said on Wednesday. The ECB has kept up pressure on cash-strapped Greece in recent months by capping the amount of Treasury bills the country's banks are allowed to hold, effectively cutting off the government's main borrowing channel. ...