travis installation may timeout due to scipy

[johnyf]

For example, a Travis build can take 10 min.
Support for a pre-installed scipy is discussed in travis-ci #2650. This issue is a note that slow builds are normal, and a reminder to install numpy and scipy with apt and use system-wide site packages, until Travis offers a pre-installed scipy.

[slivingston]

This is relevant to a comment on tulip-control/tulip-control#131

[johnyf]

I tried using system site packages and installing python-scipy, in addition to python-numpy. Whereas this delivers numpy == 1.6.1 (numpy >= 1.6 required in install_requires, as of 4b3d1c3), it gets only scipy == 0.9.0 (scipy >= 0.16 required).

The scipy >= 0.16 requirement (introduced in bd1b30c) cannot be relaxed to 0.9.0 (2011), because scipy.optimize.linprog appears to have been introduced later (2013).
So, pip install scipy cannot be avoided.

I used travis_wait 30 pip install scipy (minutes) to address the timeout in 74f1a8c.

In the future, a descent solution would be to build a Linux wheel (only OS X wheels are available for scipy on PyPI), and place it somewhere convenient, so that we pip install that on Travis.