Fix python reference and imports

[tristil]

I wanted to use task.shift-recurrence but ran into these issues on MacOS.

• Use env to select the right python executable. Fixes issue on MacOS
  with selecting the system python instead of the Homebrew python.
• Existing imports did not work using the development version of tasklib
  mentioned in the README.

[tbabej]

The executable change I'm fine with, however, the imports seem to be working for me. I tested the issue in a new, clean virtualenv:

$ mkdir testenv
$ cd testenv/
$ virtualenv .

New python executable in ./bin/python2
Also creating executable in ./bin/python
Installing setuptools, pip...done.
$ bin/python2.7
Python 2.7.10 (default, Sep  8 2015, 17:20:17)
[GCC 5.1.1 20150618 (Red Hat 5.1.1-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import tasklib
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named tasklib
>>>

$ bin/pip2.7 install git+git://github.com/tbabej/tasklib@develop
You are using pip version 6.0.8, however version 7.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
Collecting git+git://github.com/tbabej/tasklib@develop
  Cloning git://github.com/tbabej/tasklib (to develop) to /tmp/pip-yICyT9-build
Collecting six==1.5.2 (from tasklib==0.10.0)
  Using cached six-1.5.2-py2.py3-none-any.whl
Collecting pytz (from tasklib==0.10.0)
  Downloading pytz-2015.7-py2.py3-none-any.whl (476kB)
    100% |################################| 479kB 317kB/s
Collecting tzlocal (from tasklib==0.10.0)
  Using cached tzlocal-1.2.tar.gz
Installing collected packages: tasklib, tzlocal, pytz, six
  Running setup.py install for tasklib
  Running setup.py install for tzlocal
Successfully installed pytz-2015.7 six-1.5.2 tasklib-0.10.0 tzlocal-1.2

$ bin/python2.7
Python 2.7.10 (default, Sep  8 2015, 17:20:17)
[GCC 5.1.1 20150618 (Red Hat 5.1.1-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from tasklib import TaskWarrior
>>>

[tristil]

Weird. I'm getting this locally:

 sh-3.2$ pip2.7 install --user git+git://github.com/tbabej/tasklib@develop --upgrade
Collecting git+git://github.com/tbabej/tasklib@develop
  Cloning git://github.com/tbabej/tasklib (to develop) to /var/folders/pm/64xc5hqn3qqc0xwrh04wzsjc0000gn/T/pip-cd4I4R-build
  Requirement already up-to-date: six==1.5.2 in /usr/local/lib/python2.7/site-packages (from tasklib==0.10.0)
  Requirement already up-to-date: pytz in /usr/local/lib/python2.7/site-packages (from tasklib==0.10.0)
  Requirement already up-to-date: tzlocal in /usr/local/lib/python2.7/site-packages (from tasklib==0.10.0)
  Installing collected packages: tasklib
    Running setup.py install for tasklib
    Successfully installed tasklib
sh-3.2$ task add test
Traceback (most recent call last):
  File "~/.task/hooks/on-add-pirate", line 7, in <module>
      from tasklib.task import TaskWarrior, Task
      ImportError: cannot import name TaskWarrior
      Hook Error: Expected feedback from a failing hook script.

I'll investigate on my own. In the meantime I dropped those changes and left just the executable change.

[tbabej]

I figured out where the difference is, I am importing:

>>> from tasklib import TaskWarrior

and you are (this is in the codebase)

>>> from tasklib.task import TaskWarrior

The code in the repository contains the wrong version.

Can you please get the import commit back up again, only not importing from backends directly, as TaskWarrior is exposed in the main module?

I think we'll be fine for merging then. If you'd prefer doing it in a different pull request, feel free to do so.

[tristil]

@tbabej Sure. Commit added.

[tbabej]

Thanks!

[tristil]

np, thanks for task.shift-recurrence