Fixes broken build in VS2013 introduced by
18bd810228. That commit attempted to fix a
compiler warning from VS2015, but this turns out to be a compiler bug:
https://github.com/dotnet/roslyn/issues/4027 . That commit added code
which VS2013 correctly treats as a compiler warning, breaking the VS2013
build.
I have reverted this unnecessary change to the deflate code, fixing the
VS2013 build, and disabled warning CS0675 on send_bits() which will
satisfy VS2015.
