PMJS should run files in script mode, shouldn't try to retrieve the last expression value of the file

[Xmader]

If the last expression value is a JS type that can't currently be converted to a Python type in PythonMonkey
(e.g. JS Symbol type),
pmjs should ignore it completely instead of trying to covert it so hard (segfault/error).

[Xmader]

The main change in this PR is

PythonMonkey/python/pythonmonkey/require.py

Line 412 in 91355f2

pm.eval(mainModuleSource.read(), {'filename': fullFilename, 'noScriptRval': True})

---

Test file:

// pr362.js
console.log(Symbol('abc'));
Symbol('xxx');

Without the 'noScriptRval': True change in require.py

With the change: