A phase II Open Label, Multicentre, Single Arm Study to Characterise the Efficacy, Safety and Tolerability of Gefitinib 250 mg (IRESSA�) as 3rd line treatment re-challenge in Patients, who have Epidermal Growth Factor Receptor (EGFR) Mutation Positive Locally Advanced or Metastatic Non-Small Cell Lung Cancer (NSCLC) and who responded to gefitinib in 1st line and progressed after 2nd line chemotherapy