--include-path does not work with Rhino

[gdelhumeau]

2 problems:

• os.type() does not exist with Rhino (at least with the LESS CSS Compiler for Java). It seems it is specific to NodeJS, but I don't know Javascript enough to be sure.
• when I fix the first point, I realize that the less.Parser.fileLoader() function defined in rhino.js does not handle the path setted by --include-path.

I am proposing a pull request to fix both.