python-multiprocessing: adding runtime dependencies

python-multiprocessing: adding runtime dependencies

As python-multiprocessing requires python-threading and
python-pickle, this commit adds them as runtime dependency.

The observed behavior was:

When typing 'import multiprocessing' in the python shell on a
minimal image with only the python-multiprocessing recipe installed,
python reports at first:

Python 2.7.3 (default, Jun 27 2013, 08:26:25)
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import multiprocessing;
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/multiprocessing/__init__.py", line 65, in <module>
    from multiprocessing.util import SUBDEBUG, SUBWARNING
  File "/usr/lib/python2.7/multiprocessing/util.py", line 38, in <module>
    import threading        # we want threading to install it's
ImportError: No module named threading

After adding python-threading as runtime dependency and rebuilding
the image, python reports:

Python 2.7.3 (default, Jun 27 2013, 08:26:25)
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import multiprocessing;
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/multiprocessing/__init__.py", line 84, in <module>
    import _multiprocessing
ImportError: No module named cPickle

(From OE-Core rev: e913412ca0ff01cb654757c8199e8859f15b7cf7)

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@oss.bmw-carit.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>