UPDATE 3-Armenian president wins re-election, exit poll shows

* Sarksyan had big lead in polls before vote * Incumbent had promised stability * Campaign tainted by assassination attempt on rival (Adds quotes, background) YEREVAN, Feb 18 (Reuters) - Armenian President SerzhSarksyan easily won a new five-year term on Monday, an exit pollshowed, in an election overshadowed by a lack of seriousopposition and an attempt to kill a minor candidate. The opposition ...