ATHENS (Reuters) - Greek banks suffered steep losses for the third say in a row on Wednesday, with two -- Alpha Bank and Piraeus Bank -- effectively down to the 30 percent loss level at which trading in them is halted. The overall banking sector index was down 23.6 percent, adding to near 30 percent falls on Monday and Tuesday. Greek banks are in dire need of recapitalisation after a flight of euros from deposits for most of this year and mounting loan impairments. But such recapitalization, when it comes, will hurt existing shareholders. ...