Its name is Trigger. No, not Roy Roger’s horse, but Willie Nelson’s guitar. The Texas country singer named his guitar after Roy’s horse, so there is a natural kinship between them. Willie has been playing Trigger since 1969. It has been with him for over 10,000 shows, 85 studio albums, and hundreds of thousands of miles. His pick has worn a sizable hole on the front of the guitar, and hundreds of people have signed their names on the guitar,…