If node isn't installed, setup.py develop will fail part-way through

the installation process. However, if it's installed but as nodejs

(such as on Ubuntu), it will all work correctly until you go to run

Review Board, at which point it will fail confusingly when it fails to

find node in the path.
We now check for both node and nodejs, and provide appropriate error

messages depending on what we find or don't find.

Tested with node in the path and without.
Tested without node in the path but with and without nodejs in the

path.
Saw the expected behavior in all cases.