By Jonathan Spicer ISTANBUL (Reuters) -Sweden has taken “concrete action” to address Turkey’s concerns over its NATO membership bid, including stepping up counter-terrorism efforts against Kurdish militants, Stockholm told Ankara in a letter dated Oct. 6 and seen by Reuters. The two-page letter gives 14 examples of steps taken by Sweden to show it “is fully committed to the implementation” of a memorandum it signed with Turkey and Finland in June, which resulted in NATO member Turkey lifting its veto of their applications to the trans-Atlantic security alliance. Sweden and Finland launched the…