Fix problems with connection recycling and recovery.

We were incorrectly attempting to recycle connections terminated by the end
of a socket stream.

And we were keeping the 'Accept-Encoding: gzip' header on a recovered request,
which was suppressing our transparentGzip flag from getting the 'true' value
it requires.
Merge pull request #632 from square/jwilson_0310_recover_from_failures

Fix problems with connection recycling and recovery.