Add failing tests for first part of #213
Reproduce the previous test failure w/o stdlib

It turned out that the failure occurs when you define "fake module path"
by importing some module from others.  Indeed, this is what happens
in os.py.
merge issue-213-from-import-definition of @tkf into dev
finding out that fake imports arent't allowed in python and os.path is a sys.modules modification, fix tests #213
fix a nested import problem with not found imports
os.path is now accessible, but nested imports in general are not. fixes #213, #230
use ImportPath.is_relative_import instead of complicated lookups all the time
minor refactoring, use finally instead of complicated except
use docopt for run.py executions, much more readable
fix a few debugging problems