BOISE, Idaho (Reuters) - Pregnant mothers caught using illegal drugs could go to prison for endangering their unborn children under a bill passed by the Idaho State Senate on Tuesday. "The first thing we're after is a drug-free baby," said State Sen. Denton Darrington, a Republican who said his eastern Idaho district is plagued by methamphetamine use. "Meth is a problem everywhere in the state of Idaho." If the measure passes the Idaho House and receives the approval of Idaho Gov. Dirk Kempthorne, a Republican, the measure would be the first in the United States specifically to make it a...