(Reuters)-AppleInc'ssharesfellbyasmuchas12percentonThursday,stagingtheirbiggestpercentagedropinoverfouryearsandslicingmorethan$50billionfromthecompany'smarketvalue,asdisappointingholiday-periodiPhonesalesreinforcedfearsitislosingitsdominanceinsmartphones.Eighteenbrokerages,includingBarclaysCapital,MizuhoSecuritiesUSA,CreditSuisse,andRaymondJamescuttheirpricetargetsonthestockofthew...