Pickle fails in REPL

This is a bit of a nitpick, but in the interest of total python compatibility:

When the following code is run in the coconut interpreter it fails:

```
import pickle

class C(object): pass

myC = C()

print(pickle.dumps(myC))
```

with

```
>>> print(pickle.dumps(myC))
Traceback (most recent call last):
File "c:\users\oscil\documents\coconut\coconut\coconut\command\utils.py", line 106, in run
return run_func(code, self.vars)
File "c:\users\oscil\documents\coconut\coconut\coconut\command\utils.py", line 68, in try_eval
return eval(code, in_vars)
File "", line 1, in
_pickle.PicklingError: Can't pickle : attribute lookup C on __main__ failed
```

In the python interpreter, it yields the following, as is should:

```
>>> print(pickle.dumps(myC))
b'\x80\x03c__main__\nC\nq\x00)\x81q\x01.'
```

However when compiled with coconut it works.

I think this has something to do with the main module not being registered correctly for pickle to work.