Conduit: apply the Vchan.In_memory module in addition to the network stack

This Vchan dependency being hardcoded should still work fine on Unix,
since it just defaults to the loopback Vchan model.  We will make it
disappear in a future revision that uses open types to avoid having all
the supported transport mechanisms appear as a functor argument.
Adjust http test for conduit api
travis: reduce verbosity slightly
Merge pull request #297 from avsm/master

Conduit: apply the Vchan.In_memory module in addition to the network stack