Fix #438 - don't use Unix pipes for our commands, use node pipes

[humphd]

This fixes npm start and npm test so you don't need to use a pipe at all. It also fixes a bug in habitat, where you can't overwrite a variable in your env with something in the environment.

[Pomax]

npm start works, npm test has issues with mocha:

Running "exec:run_mocha" (exec) task
>> 'node' is not recognized as an internal or external command
>> operable program or batch file.
>> Exited with code: 1.
Warning: Task "exec:run_mocha" failed. Use --force to continue

[humphd]

@Pomax, @alicoding: I think I have this fixed, r?

[alicoding]

r=me with travis

[humphd]

Travis is good, @Pomax if you could actually try this on Windows, I'd feel better.

[alicoding]

tested on Windows 10 and ran the test with no problem.