NEWYORK(Reuters)-IftheUnitedStatessailsoverthefiscalcliffinlessthantwoweeks,itprobablywillnotmeandisasterforthestockmarket,investorssaidonFriday,butthemarginforerrorisgettingdangerouslythin.AtheartarefearsoverhowlongtheU.S.economy,theworld'slargest,canholdupunderthebruntofhighertaxesandbigspendingcutsthatwouldbetriggeredbythefiscalcliff.IfWashington'sinabilitytoreachadeficit-reduc...