Use `__halt_compiler()` to stop PHP processing

Rather than die, call [__halt_compiler](http://php.net/manual/en/function.halt-compiler.php) to stop PHP processing the file. This way, if the file is accidentally accessed, there won't be a bunch of errors about classes existing, etc.
Merge pull request #2 from alexrussell/patch-1

Use `__halt_compiler()` to stop PHP processing