Detect and report hashbag as unsupported

Created by: ozten

If I run sjs over a NodeJS source which has #!/usr/bin/env node then I get the error

Error: Line 1: Invalid regular expression

I wasn't able to find a clean way to remove the offending line from the source and continue parsing.

Perhaps throwing a more direct error message? This PR would instead give the error

Error: Line 1: HashBang interpreter directive is not supported