Compress most replies if client accepts gzip

If the user agent announces it can accept gzip encoded replies,
gzip before sending to save on transfer bandwidth.

Streaming HTML responses are never gzip compressed. Individual
writes may be small and become stuck in the gzip compression path,
causing unexpected latency to view new results as they are output
by the servlet.

Change-Id: I4cde58793443c29960f7211378a27e0c29de7dac
2 files changed