AsyncTarget wrapper flushed events when closed
AsyncTarget wrapper flushed events when closed

Currently the AsyncTargetWrapper didn't flush events when closed, which
could lead to missed messages.
fixes #134

rajk987/NLog,blair55/NLog,BrandonLegault/NLog,rajk987/NLog,nazim9214/NLog,ajayanandgit/NLog,czema/NLog,mikkelxn/NLog,UgurAldanmaz/NLog,littlesmilelove/NLog,bryjamus/NLog,rajeshgande/NLog,rajk987/NLog,zbrad/NLog,snakefoot/NLog,vladikk/NLog,czema/NLog,ie-zero/NLog,pwelter34/NLog,AqlaSolutions/NLog-Unity3D,tetrodoxin/NLog,RichiCoder1/NLog,luigiberrettini/NLog,sean-gilliam/NLog,Niklas-Peter/NLog,UgurAldanmaz/NLog,AndreGleichner/NLog,thomkinson/NLog,fringebits/NLog,vbfox/NLog,bhaeussermann/NLog,blair55/NLog,Niklas-Peter/NLog,luigiberrettini/NLog,BrutalCode/NLog,tohosnet/NLog,MoaidHathot/NLog,hubo0831/NLog,tmusico/NLog,FeodorFitsner/NLog,michaeljbaird/NLog,pwelter34/NLog,fringebits/NLog,tmusico/NLog,BrandonLegault/NLog,MoaidHathot/NLog,zbrad/NLog,bryjamus/NLog,matteobruni/NLog,littlesmilelove/NLog,breyed/NLog,FeodorFitsner/NLog,nazim9214/NLog,blair55/NLog,babymechanic/NLog,tohosnet/NLog,czema/NLog,bhaeussermann/NLog,blair55/NLog,blair55/NLog,fringebits/NLog,hubo0831/NLog,BrandonLegault/NLog,ajayanandgit/NLog,michaeljbaird/NLog,AqlaSolutions/NLog-Unity3D,vladikk/NLog,BrutalCode/NLog,campbeb/NLog,babymechanic/NLog,czema/NLog,NLog/NLog,mikkelxn/NLog,RRUZ/NLog,campbeb/NLog,RRUZ/NLog,thomkinson/NLog,ie-zero/NLog,AqlaSolutions/NLog-Unity3D,kevindaub/NLog,thomkinson/NLog,ArsenShnurkov/NLog,blair55/NLog,MartinTherriault/NLog,ArsenShnurkov/NLog,bjornbouetsmith/NLog,matteobruni/NLog,vbfox/NLog,RichiCoder1/NLog,AndreGleichner/NLog,304NotModified/NLog,AqlaSolutions/NLog-Unity3D,vladikk/NLog,mikkelxn/NLog,ilya-g/NLog,ilya-g/NLog,MartinTherriault/NLog,vladikk/NLog,tetrodoxin/NLog,mikkelxn/NLog,bjornbouetsmith/NLog,rajk987/NLog,BrandonLegault/NLog,thomkinson/NLog,breyed/NLog,rajeshgande/NLog,fringebits/NLog,kevindaub/NLog