node: add support for --interactive-eval (-ie) flag

Fixes #1197 (closed)

This achieves the desired -ie behaviour of pre-loading the eval expression into, and opening the repl.

iojs -ie "var life = 42"
undefined
> life
42
> 

iojs -ie "console.log('hello world')"
hello world
undefined
> 

I'll setup a test in test-repl-options if this looks reasonable, also, not sure if this needs to be documented in --help or not.

Edit: another thing, what subsystem: should this be?

/cc @bnoordhuis /first time I've ever touched C++ \o/