HTTPSock: Gzip compression for static files (text/* mime types + files
with .js extension) and dynamic HTML responses (if gzip is available and
the compression method is supported by the requesting HTTP client).
Get rid of empty CHTTPSock::WriteFileGzipped method if there's no zlib. It's still in the header, but this does not have any negative side effects.
Merge commit 'refs/pull/306/head' of github.com:znc/znc