BELGRADE (Reuters) – Protesters have pitched tents in front of Serbia’s presidency building demanding a halt to lithium exploration on environmental grounds, fearing a project that has its licence revoked will be resurrected after April’s election. The protest is a headache for the ruling Serbian Progressive Party ahead of the vote expected on April 3 and, combined with rising fuel and food prices, threatens to dent its popularity. Thousands of people blocked roads last year to demonstrate against the government’s backing of Rio Tinto’s $2.4 billion Jadar project, forcing the local municipalit…