CARACAS, Venezuela (Reuters) - A bomb exploded in western Venezuela near the frontier with Colombia on Wednesday, damaging the headquarters of a local ranchers' association which had denounced cross-border activity by leftist Colombian rebels, witnesses and police said. No one was injured in the early morning explosion which tore through the car park and the entrance of the building in San Cristobal in Tachira state, shattering windows and scattering debris. Officials said two men were arrested in connection with the explosion. The blast came four days after a bomb badly damaged a Caracas office building where Venezuelan government and opposition...