Revive lookfor magic

Hello,

This PR enables the lookfor magic which has been dropped in 0.13.x:
https://github.com/ipython/ipython/blob/0.13.x/IPython/quarantine/ipy_lookfor.py

The syntax is:
%lookfor [-r] what modules

An example:
{{{
Search results for 'transpose'
------------------------------
scipy.ma.transpose
    Permute the dimensions of an array.
scipy.chararray.transpose
    a.transpose(*axes)
scipy.cov
    Estimate a covariance matrix, given data.
scipy.transpose
    Permute the dimensions of an array.
scipy.einsum
    Evaluates the Einstein summation convention on the operands.
scipy.loadtxt
    Load data from a text file.
scipy.matrix.getT
    Returns the transpose of the matrix.
}}}

I'm not sure about how to test it properly though, could I get your feedback on this ?