Junta chief Prayut Chan-O-Cha formally became Thailand's 29th prime minister Tuesday after a royal endorsement, completing a long transformation from soldier to civilian leader and vowing "love, unity and compassion".But critics may doubt the divisive leader's pledge after his previous stint in power which was marked by a ban on political gatherings, a clamp down on the media and the muzzling of dissent.The 65-year-old ex-army chief led the 2014 coup, the last of