partial progress on refactor of response handling
remove unused test
more changes to error handling
clean up response decoding
fixes for latest nightly
replace .or_else with .map_err
Fix travis build

per http://bettong.net/2014/05/09/how-to-test-rust-on-travis-ci/
Read length of response as u32 instead of i32

This is what the official drivers do, in spite of what ql2.proto says
and is consistent with protob.cc in the rethinkdb source. Also just cast
to uint instead of wrapping + unwrapping.