Relative paths

This is the set of changes required to make SCons and Emscripten play together on Windows with Win32 NodeJS and Cygwin Python.

Comments?

If that is the underlying issue, then let's fix the path in jsrun right before calling node? that way, we are not vulnerable to bugs where the cwd changes. That is, we would keep using absolute paths in python, and in the single place where we go from python to node, we convert the path, using the current cwd.