Try a fix for issue 24

This MR will check if the __loader__ is not None before attempting the hack. Closes #24 (closed).

@amohammadi: please check - use a bootstrapping config file before attempting buildout:

[buildout]
parts =
develop = src/bob.buildout

Do:

$ buildout -c first.cfg #as per above
...
$ buildout

Notice your buildout.cfg should contain the develop entry src/bob.buildout so to use the checkout bob.buildout instead of the default one.

If that fixes your problem, please merge this.