Make sure we always read the body of a PUT or POST request

Unfortunately if a PUT or POST request that has a body fails to
read it then Apache will sometimes fail to return the response it
is given to the client properly, instead erroring:

  https://issues.apache.org/bugzilla/show_bug.cgi?id=44782

To work round this we call rewind on the body for every request using
a filter, which forces it to be fetched from Apache into a file.