Merge pull request #57 from malaporte/buffer-and-client-fixes

A few fix plus missing 'constants' core module
Arrange for the JS code to initially run in an event loop thread, to avoid several different loops being created that could then execute code at the same time.

I also added a check to ensure that .end on an internal http client request is called only once, since NodeJS seems to tolerate that and I've caught npm modules doing it.
Merge branch 'fix-event-loop' into coveo
Convert numeric header values to string before calling putHeader.
Merge branch 'fix-numeric-header-values' into coveo
Use our own internal versions of DynJS and jvm-npm for now.