By Richard Martin, BARCELONA, Sept 7 (Reuters) - Chris Froome still faces a near-impossible task in his bid to catch leader Nairo Quintana after finishing alongside the Colombian in stage 17 of the Tour of Spain, which was won by Swiss rider Mathias Frank. Froome risked losing even more ground as he struggled to keep pace with Colombians Quintana and Johan Esteban Chaves and Spaniard Alberto Contador, but the Briton caught up with the trio late on to finish 25th. More...