A randomized, double-blind, placebo-controlled, parallel group, multi-center, multiple dose (7 days) dose-ranging study, to assess the efficacy and safety of 4 doses of QAB149 (50, 100, 200 & 400 µg) delivered via a multiple dose inhaler and 1 dose of QAB149 (400 µg) delivered via a single dose inhaler in patients with chronic obstructive pulmonary disease (COPD)