JAMAICAN dancehall star Vybz Kartel asked a London court to overturn his murder conviction, citing attempts to bribe his trial jury and the use of incriminating messages as reasons his conviction is unsafe. The musician, whose real name is Adidja Palmer, is one of Jamaica's most popular artists and has collaborated with performers such as Jay-Z and Rihanna. Kartel, 48, has been in jail in Jamaica since 2011 when he was arrested over the disappearance of his associate Clive "Lizard" Williams, whose body has never been found. After a 64-day trial in Kingston, one of the longest in Jamaican history,…