Document keep alive and include new timeout in response

o Report new expire time after refreshing transaction timeout
o Due to streaming of results the new expiry time cannot be set in the header
o Updates documentation
o Ensure rollbackSuspended is called with a minimum timeout of 500 ms
o Adds sleep(3000) to two tests due to textual timestamp formats only having seconds resolution
o Use RFC1123 format similar to established HTTP Expires header
Merge pull request #824 from boggle/2.0-timeout-rest

Document keep alive and include new timeout in response headers