Added optional callback argument to flush method. Count bytes written to RequestHandler internal buffer instead of concating and getting size of that.
Added optional callback argument to flush method. Count bytes written to RequestHandler internal buffer instead of concating and getting size of that.

zcsteele/turbo,zcsteele/turbo,YuanPeir-Chen/turbo-support-mipsel,luastoned/turbo,YuanPeir-Chen/turbo-support-mipsel,luastoned/turbo,mniestroj/turbo,ddysher/turbo,kernelsauce/turbo,ddysher/turbo