KATHMANDU (Reuters) - Nepal stood on the brink of fresh political turmoil on Sunday as wrangling over the young Himalayan republic's first federal constitution ground towards a midnight deadline. A new constitution is widely seen as crucial to helping end the instability that has plagued Nepal since the end of a Maoist-led civil war in 2006 and subsequent overthrow of the monarchy, but it has been thwarted by demands for the country to be divided into states along ethnic lines. ...