Install python packages from repository cache instead of from PyPi directly.

This will make it possible to build without needing an internet connection,
speeding things up as well as maintaining better control.
Merge remote-tracking branch 'breznak/pip-install' into cached-externals
Minor spelling correction
Merge pull request #138 from oxtopus/cached-externals

Cached externals
modular: numpy - remove source dirs

for linux and MacOS
numpy: use pip install dependency

numpy 1.6.2 was/is used
modular numpy: dont copy files,

pip already instelled them in proper location
numpy installed by pip fix includes
numpy: update to the latest stable version

from 1.6.2 -> 1.7.1
release notes http://sourceforge.net/projects/numpy/files/NumPy/1.7.0/
add source tarball for numpy to pip cache