Fix #1016: Respect NODE_PATH from the environment.

In order to be able to use normal Node.js modules, the NodeJSEnv must
respect NODE_PATH from the environment and properly merge it with its
own provided library path (for CommonJS-style includes).
Add auto-generated tests for source maps.
Merge pull request #1007 from gzm0/sourceMapTests

Added auto-generated tests for source maps.