Don't change the defaul log level during import. Otherwise, the user can't get the log level he want during theano import.

fix gh-2130
remove import/variable not used (and add a missing warnings imports).
[CRASH] Fix recent compilation crash.
Remove a file under Apache licence (argparse)

Argparse is in Python 2.7. This file was added for compatibility with
older python.

We remove one of its user(nose_pr.py) that we don't use.

As we support python 2.6, I raise a good error message in the only
file that use it. As it is available in pypi, I think it is fine we
don't provide it for python 2.6, as this file isn't very important.
Set back the default INFO logging at one place, but only if the user didn't specify one.
Merge pull request #2143 from nouiz/log

Don't change the defaul log level during import. Otherwise, the user can...