Requires class attribute to be last

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Create an Instances object where the class attribute is not the last 
attribute.
2. Try to build a classifier using FastRandomForest.

What is the expected output? What do you see instead?
NullPointerException

What version of the product are you using? On what operating system?
0.99

Please provide any additional information below.
It works fine if the Instances object is altered to make the class attribute 
last. All classifiers bundled with Weka can handle the class anywhere in the 
list of attributes, so this one should be changed to do that as well.

Original issue reported on code.google.com by [email protected] on 21 Feb 2014 at 2:02