(Adds Syrians allowing U.N. aid convoy into besieged district in Homs) BEIRUT, **v 11 (Reuters) - The United Nations peace envoy to Syria said on Tuesday that Syrian officials had given him positive signals on a U.N. proposal for a local truce in the **rthern city of Aleppo, a main battleground in Syria's three-year-old war. Speaking in a news conference in Damascus after meeting President Bashar al-Assad and the Syrian foreign minister, Staffan de Mistura said the government's initial response to the proposal "was of interest, and constructive interest". ...