Move module-running logic from sjs -> stratified-node.js so it can be used from other nodejs scripts
BREAKING: leave `process.argv` alone (we used to remove the first argument).

This affects all command-line parsing code (although dashdash has been updated to do the right thing by default).

Introduced `sys.argv()`, which returns just the actual args (without node or SJS main module paths).
We should use this wherever possible, as it's future-compatible with new runtimes.