Input check

Today we don't do any check in the inputs.

Would be handy to have some checks (NaN, Inf) before the training.

mentioned in issue bob.learn.libsvm#9 (closed)

mentioned in commit 0c3971fa

mentioned in merge request !24 (merged)

mentioned in commit d810b588

mentioned in commit 80ceaa89

mentioned in commit 16c6ff5d

closed