'**SUMMARY**
Returns the square-form of pairwise distances for the featureset.
The resulting N x N array can be used to quickly look up distances
between features.
**RETURNS**
A NxN np matrix of distance values.
**EXAMPLE**
>>> img = Image("lenna")
>>> feats = img.findBlobs()
>>> d = feats.distancePairs()
>>> print d'

def distancePairs(self):

    return spsd.squareform(spsd.pdist(self.coordinates()))
