Fix memory leaks in the svm bindings.

It's sometimes hard to know if a particular object is being freed by
libsvm or if it's up to us to free them.

From: Fabian Pedregosa <fabian.pedregosa@inria.fr>

git-svn-id: https://scikit-learn.svn.sourceforge.net/svnroot/scikit-learn/trunk@566 22fbfee3-77ab-4535-9bad-27d1bd3bc7d8