ENH Update URL & make curl call follow redirects

Also, ignore downloaded data.

Author: luispedro

ch08/data/.gitignore

@@ -0,0 +1,3 @@
+retail.dat.gz
+ml-100k.zip
+/ml-100k/

ch08/data/download.sh

@@ -1,4 +1,4 @@
 #!/usr/bin/env bash
-curl -O http://www.grouplens.org/system/files/ml-100k.zip
+curl -L -O http://files.grouplens.org/papers/ml-100k.zip
 unzip ml-100k.zip
-curl -O http://fimi.ua.ac.be/data/retail.dat.gz
+curl -L -O http://fimi.ua.ac.be/data/retail.dat.gz

ch08/load_ml100k.py

@@ -11,6 +11,10 @@ def load():
     Returns the review matrix as a numpy array'''
     import numpy as np
     from scipy import sparse
+    from os import path
+
+    if not path.exists('data/ml-100k/u.data'):
+        raise IOError("Data has not been downloaded.\nTry the following:\n\n\tcd data\n\t./download.sh")
 
     # The input is in the form of a CSC sparse matrix, so it's a natural fit to
     # load the data, but we then convert to a more traditional array before